Always room for improvement, for match up tips, teamfight tips, deeper explanation on certain items, especially those under a lot of debate and dispute. There are the options of alternative runes, mastery pages. You stated yourself that depending on the enemy, a revolver might or might not be efficient. These are all things that could be stated.

A tanky caster still can have a deathcap, and with Swain, it is quite efficient with it. Nor does anyone think he is a burst caster.

Having increased damage on Swain raises his stamina as much as having a bit more health. In the longer run, a deathcap would generally heal more and hit harder.

This is merely opinion, but I do play Swain quite often.

At which point is this guide unfinished? I don't think that an early Hextech Revolver is a good item of Swain, especially in the early or when he has opponents like LeBlanc or Ahri whose can burst you in an instant. I think Swain isn't made to be a bursty caster, more like a tanky caster.
Not even three minutes ago I fought three people at the same time under a tower and only two people survived: me and an opponent. The stamina of a Swain is insane and that is how I like to play him.
I guess this platform isn't made so that each guide should be the same.

I play Swain often in high level gaming and in normals. First things first on your mastery tree, the reason you get points in Brute Force is because a common lane-tactic for Swain is to use your Torment then follow up for 2~ or so physical attacks for some strong harass. You don't need 4 points in the AP, you said your self you are a utility tanky caster. Instead, putting 1 point into the summoner's skill for ignite, and 3 points in brute force the help in Last hitting+Harass is much better then 4 flat AP.

You should consider getting an early Revolver for the Spell Vamp, and in many games, a Rylai's is unnecessary. Even as a utility tanky caster, you are still a caster and the extra slow isn't worth losing out on quite a bit of damage. The slow is only useful in a team lacking the CC, but as a team's AP caster, you a deathcap helps quite a bit where your magic damage becomes a threat almost instantly, rather then over time.

The guide isn't finished, so you made a huge mistake. Publishing it early makes it so you lose your 'fresh guide' chance on the first page as people who visit will only see an incomplete guide. Not to mention the countless people that'll downvoted/no vote at all.

For now, no vote on my part as the guide seems unfinished, and I'll come back to check it.

I don't agree with your item build. Where's the Rabadon's? Where's your Unholy Grail? Rod of Ages is needed, yes. But Rylai's should be replaced with an Unholy Grail. A Zhonya's: obvious. Will of the Ancients, too.

In the other items section. I play Swain more as a utility tanky caster rather a bursty mage. But it depends on the situation.

Everything ok, but where's rabadon?