I was planning on playing Hubris/Atonement and I have something I haven't grasped from the torrents of threads I read.
Living on a floating platform: does it spare me of taint? How? Doesn't it climb? Do I get a cobblestone pillar surrounded by ladders? What?
Tainted fibers will spread up nearly
any solid block. The only thing that will stop them, as far as I know, is a sealed room made entirely of artificial materials (wood planks, cobblestone, glass, doors, etc.) or an air gap two blocks wide, if not three. So to keep your island taint-free, you'll want to completely disconnect it from the ground. If you don't have access to flight yet, you could use a TiCo drawbridge to bridge the gap temporarily when you need to, and as long as you make sure to retract it when you're across, no tendrils should be able to spread across. Alternatively, you could just jump across, perhaps assisted by TiCo slime blocks.
Do keep in mind that your alchemical mistakes on the island can create tainted fibers out of nothing. If that happens, you'll just have to clean it up before it spreads. Quickest way is with a bucket of water- clicking the bucket on a tainted fiber will replace it with a water source block, which you can then pick back up.
Or, if you've progressed far enough in the mod, you could just slap down an Ethereal Bloom. They untaint all the biomes within eight blocks or so, destroying any and all tainted fibers and whatnot from bedrock to skybox.
That's assuming you're running TC4. If you're on Minecraft 1.8 or 1.9, your mileage may vary.