Well... GH has posted pics of the new Artoo. He is forever stuck in three-leg mode. The middle leg appears to be a spring-loaded button of some sort. Not sure about that though.
There are rockets on his legs and those are, thankfully, removable this time around. There is also some sort of "arm" that attaches to the top of his dome and is used for grabbing the pile of damaged droid parts that comes with him. In the droid parts you can see, there is a protocol droid head and a super battle droid midsection. There may be some other things there, but the protocol droid head is what intrigued me the most.
So... we can possibly determine a couple things based off of this figure.
1) Artoo uses his rockets in ROTS.
2) Artoo has another appendage inexplicably housed within his dome.
3) Threepio gets blown to bits at some point during the film (let's hope that it was just a generic protocol droid and not our beloved golden boy).
Oh... Artoo is also packed with some sort of base or ramp of sorts.