I agree that Kassadin should go jungle. But i think it's really hard for him to farm pre lv6 and it takes so long to reach lv16 for a jungler. (because 3 second is so much better than 7 or 5 second right?)
I don't think that we should play him in lanes because his damage is not enough now(maybe top lane??).
I think RIOT will buff him in the future
STILL +1

You don't know what you're talking about.

Kassadin jungle IS unviable. Any competent jungler can turn up in your jungle and, because you're a low mobility, will be able to catch and kill you with ease. He has slow clear times and his ganks are non-existent pre-6 (this is the same for Mid Kassadin too, so no different for jungle - no gap closer, no hard CC). So basically by locking in jungle Kassadin, you are saying to your team - 'expect no ganks for about 10 minutes'.

You misunderstand why RoA is inefficient.

1) It's extremely expensive for a jungler to build, meaning it's far more delayed than you would if you got it in mid-lane, meaning it sets you back a LONG time and you won't reach the most efficient point until about 30-40 minutes into the game (if that).

2) xPeke can build two RoAs because, guess what? HE'S PLAYING MID-LANE. He gets a good gold income and by the time he hits 6 (faster than jungle, I might add), his roam is already insane and he can build and charge a RoA by 20 minutes. Playing Kassadin midlane will still give better gold flow than jungle, because you can still farm under turret.

Again, Tear is inefficient because its stacks are the only reason you get it, more so because his Riftwalk now scales from mana. It'll delay the Archangel's Staff/ Seraph's Embrace too much until a point in the game where it's no longer relevant, because everyone else already has 4-item builds and you're still stuck on stacking a Tear.

And all this isn't even considering that Kassadin would be REALLY **** to a invade. Think about it for a second - Mid lane Kassadin already has trouble CS-ing against pretty much all enemies, because he has trouble 1v1ing anyone until level 6. Imagine how much ****ter he'd be if a Lee Sin or a Wukong came across him in the jungle? If I saw the enemy lock in a Kassadin, I'd LIVE in his jungle. I'd counter-jungle him so hard that he'd still be level 4 when I'm level 9.

At least mid-lane can still farm under turrets and get XP that way (which, for Kassadin is more important until level 6 actually).

Also, your comparison to Fiddlesticks is also stupid. Zhonya's Hourglass is one item. Rod of Ages and Seraph's Embrace cost significantly more combined, obviously. That was the most unbalanced comparison you could ever make.

True the spell vamp doesn't proc with the W but the Life Steal does hence the inclusion of the hextech gun blade and the vampirism masteries. The jungle Item does give great sustain for AP users I prefer more to make sustain better as this is a constant issue with Kass. The reason for going a little less in the offense tree is again for the better early game sustain. Runes like Masteries are always situational and more preference based on play style but you are right it doesn’t help clear as much as it helps late game with team fights. I will try the Attack Speed Runes though and see if it help out.
The reason for the CDR in my thinking is for faster skill spamming to get the charges on void pulse. Hence Athena’s and IBG plus they offer some much needed defensive stats. It is obvious with the rework that the focus was to make Kassidin’s W and E his main damage sources. I don’t think Q has the worthy harass it once did so I tend to max this last. I‘ve always like the melee aspect of Kassidin but it could never be utilized until now. I guess we will see where he goes from here. But like I said before I like this guide for being different and trying to utilize this new Kass in a new direction. Cheers m8!

Well, spellvamp isn't usefull on him because only his Q E and R benefit from it (E and R cut to 1/3). His W is an on-hit effect and doesn't benefit from Spell Vamp. The SotSW passive: Against monsters, deal 30% bonus damage and restore 6% of damage dealt to monsters as health and 3% as mana. instead converts every part of his damage into health and mana, it is like having 7.8 spellvamp and 7.8 lifesteal that procs from his W, his main source of DPS.

Now why 21 in offense? More damage means faster jungle clear and faster jungle clear means less damage taken from monsters. We would be sacrificing havoc, and a 3% increase in damage. In fact, I think the lifesteal is more useful than the spellvamp on him, but still we are sacrificing jungle clear for that and taking more damage from monsters.

About the runes, I'm focusing on jungle clear and still trying other stuff, but AS runes are better. 15% AS means a 15% increase in your dps overall. Hybrid runes don't work in jungle clear, because monsters don't have magic resist and 4.5 will never increase your physical damage past 4.5%. Still they are obviously better for laning and killing people, but we want jungle clear. Scaling AP are definitely a choice, so I will try them.

About the rework, it left kassadin's build open to a lot of choices so i'm still looking for new build paths. But looking at his numbers,riftwalk damage is low even with a big mana pool, like a 4 stack riftwalk dealing 300+ 5% mana (assuming you have 3000 Mana) it only goes to 150 bonus damage. So stacking mana is only needed to spam riftwalk but not for its damage. I tried to focus my build in the old kassadin playstyle (throw QE and only all in when needed) because his Q and E still have the same AP ratios, but thanks for the advice and I'll keep trying new builds.

I actually have run something similar to this myself and the idea is not bad but b/c Kassadin really needs that early game pop from the offense tree it is hard to build him tanky in the mastery department with the sustain he needs. So I have a few suggestions. Go 19/0/11 or 18/0/12. Kass has no innate sustain but because he has such high scaling AP ratios as well as significant AD gains as he levels, the Vampirism mastery will allow you to sustain better and stronger. With his nerf a significant amount of damage come from his ability to AA and proc the Nether Blade active so LS and SV are excellent on him. Plus the extra sustain with damage makes his early game a lot less horrid.
Runes stay the same for me although for jungle or single lane I take 3 Marks of Attack Speed and the 6 Hybrid Pen Marks, 9 Armor Seals, 9 AP/Lvl Glyphs and the standard AP Quints.
With all this mind Kassidan still has a lot of burst even in lane but as he really has to focus that burst within mid to melee range I suggest a meatier item build. Obviously grab your jungle item but IBG is awesome to compliment. The mana helps scale your ult, excellent armor ratio to make you stronger, some AP, CDR and a slow on the sheen proc. I prefer Merc Treads so I don’t get locked down as escaping is a bit harder even on lower cool down. Core is still Seraphs Embrace, ROA (2 situational) and usually Athena’s Unholy Grail. And going with a theme of LS and SV I grab a Hextech Gunblade to give a very efficient sustain. I know this is not an AP focus but let’s be honest you can’t really afford to focus completely on AP. He is more of an AP/Fighter Mage with a secondary focus on assassination with this rework. Personally this is a good start and thank you for putting it out there.

If you're even bothering with playing kass jungle (which I strongly advice against).

That's the spirit. Don't even bother to try something and just say it is in-viable.

ROA is already efficient even without passive (10% more efficent than Zhonya's). I've seen pro's (xpeke) even get two roa's on kassadin. STACKED Tear isn't needed really until later game when you should be abusing riftwalk because your W plus spectral wraith gives enough sustain. Of course if you haven't played him in the jungle you can assume he is equally as mana starved as mid lane Kassadin.

Also consider Mid lane kassadin has hard time farming and csing at first level, so rushing roa is still hard on him anyway. It is an extremely cost efficent item by itself, and better with the passive.

Fiddlesticks doesn't need to stack a zhonya's. It's cost efficient from the get-go. If you're even bothering with playing kass jungle (which I strongly advice against) and get these items that late into the game (Since you're buying a doran's, spectral wraith and enchanted boots first) it will consequently take you ages for it to stack up. Rod of Ages needs 10 minutes and Tear 20 minutes on average. Until the moment you've finished both full items and have them fully stacked, they're not cost-efficient so if you ever plan on getting them, you need to get them early or they won't be worth it until the 40/50th minute.

They both cost 3500 and Fiddlesticks jungler must build Zhonya's at 3660.

You just cannot get Tear and ROA that late. Stacking both items will take ages since junglers are typically lower on gold.