Speculation, of course, but based on prior precedent...
I'll start:
1. Will those with grandfathered unlimited 3G data plans be able to upgrade to unlimited 4G, as AT&T has typically allowed on other devices?
My .02 on this is AT&T will be killing the grandfathered plans when the next iPhone with 4G comes out. If you look at the signs from AT&T I think its pretty obvious that unlimited data is going away for good....
4. Coke or Pepsi?
Killing it for all?
I have grandfathered on both iPhone and iPad. I would mind less if they only killed it on my iPhone.