I don't think AP skarner is really viable unless your jungling (flash smite pl0x) I completely agree surge on paper looks great for skarner, but even for solo top you need exhaust/ghost or flash/teleport, or ghost/flash
you just can't stick to targets properly without getting exhaust. This problem can be changed by getting shurleya's which i'd recommend on skarner regardless of build, it's too good to miss out on for ulty grabs.

I think a rabadons and a rod of ages would work better if your going AP, going hybrid isn't as good as it was on him, either AD offtank or AS/AP are the best now. I wouldn't say try and do both, you just won't do the damage and you won't have the tankiness to compensate.

Something like: rod, merc treads, rabadons, lich bane, nashor's, wit's end/madreds blood razor's
Guinsoo's is fine though I still rate that, maybe instead of rod if you were in a glass cannon mood.

The shield for me, is more of a Tower Destroyer and a Gap Closer/Escape Mechanism. Fracture gives me range, and easy heals at level 1. I would never take Crystal Slash at level 1, mainly due to low damage, and the fact that it's not useful unless you have Fracture as well, which IMO is a better level 1 skill. It is a reliable heal if you aren't playing super offensive, which I don't do anyway. I play defensive at early levels, and offensive after I have my ult.

I will have to try Rylai's with this build. That sounds like a brutal combo and I really love the sound of it. You bring up a great point with the slows. It would be easier to get them through basic attacks, I agree 100%. Hextech Gunblade is also an amazing item on him, and I do use it every now and again. But since I'm focused more heavily on AS/AP, I usually don't use it. I will certainly test both the items you mentioned out however, and possibly change the guide if I find that they work well within my build.

Thank you for your input.

Skarner's sustain thrives upon his shield, not his heal. You are much more durable and get much more benefit from going Shattered Earth -> Seismic Bastion -> Ixtal's Impact. More shield means you take more damage, which means you will be attacking faster for longer, which in turn also means you will get your CDs up sooner. The poke you get from the heal isn't worth it since you have to attack whatever you hit to heal. It isn't a reliable heal, is what i'm getting at.

I can understand the Lich Bane and Guinsoo's Rageblade, but without Rylai's Crystal Scepter you're always going to have a much, much harder time closing gaps and getting off the slow from Shattered Earth. Hextech Gunblade needs to be a core item too, IMO. That item alone will make him pure hybrid (which is what he's best as).