Way too early to say. I think probably a reissued / remolded Optimus Prime Leader Class, though, because I cannot see how you'd improve on what is basically the most perfect representation of the character in the Movie line. Megatron might get the same upgrade treatment, unless he adopts an Earth mode for the third movie. I'd not like to say though since it's too early in the day to even consider who the Leader Class toys for the 2010 line are. Though I'm guessing a Prime and a Megatron.
Anything that makes me go "Holy crap, this is awesome! I would have LOVED this as a kid!" instead of "Hmm, whilst I can't fault the impressive engineering, this thing has no soul and would surely lead to a child dashing it against the wall." I have no hope whatsoever that this will be the case.
If I were to venture a guess on a new character, I'd say Ultra Magnus for a TF3 Leader figure. But who knows. I really would like to see a "good" movie Leader Megatron. Maybe even just a remold of the ROTF one, with a right elbow joint and maybe have his murder arm sort of close "clam shell" style over the arm when you fold it down. You know what I mean? That alone would be a big improvement for that figure.
Ok . . . I don't have too many different ideas than the ones already previously posted, but I'll throw in my two cents. I hope to God that they don't have a leader class Bumblebee for two reasons. 1) They already have a Supreme Bumblebee that doesn't sell all that well. 2) Bumblebee is probably the most popular character and parents will always buy they're kids the cheaper deluxe Bumblebee over the expensive leader Bumblebee. So Hasbro, don't clog the shelves with a Leader BB when you can make a leader Blackout!
Here is what i think 1.Retool of Optimus 2. NEW mold for Megatron 3.Maybe soundwave or maybe grindor/the new pave low helecopter person or maybe a pretender like bludgeon. 4. Possibly a leader Rodimus/Ultra Magnus or maybe see a combiner (like landfill from RID)
Leader Optimus-ROTF REPAINT and head remold. Leader Megatron-New Mold. Leader Skywarp-Voice clip of Frank Welker,Black and Purple repaint of ROTF Screamer. Leader Thundercracker-Voice clip of Mark Oilver,Blue and Red repaint of ROTF Screamer. Leader Soundwave-With Laserbeak,Rumble,Ratbat, & Overkill. Leader Galvatron-New Mold.