^^This.
Rooting allows you to make whatever changes you want, but those changes still have to work. There's a big difference between rooting and flashing roms, however, which is the normal procedure for actually changing the entire UI. I would imagine it'll take a little while to crack the RIL, however we'll see plenty of custom roms before then.
It'd be quite easy though to root it, run Apex, Nova, or Trebuchet, and debloat some of the more resource-intensive TW apps that aren't a direct part of the framework. Make a few speed tweaks dependent on how its set up out of the box, and theme it to get rid of all the ridiculous colors and make it look like stock ICS. All this is within the capability of many users, and for those that can't, we should see simple ROM's that make these basic changes within a few days of its release.
But no, you can't merely root and just revert to stock Android. Not yet, anyway.