Blue Canoe Stew, the poster at RTM who’s been pretty accurate with his DCUC leaks so far, says the 2010 SDCC DCUC exclusive will be Plastic Man:

Plasticman with various attachments and shapes that wouldn’t normally fit on a single figure card. He’ll be the last figure needed to complete Mattel’s re-making of the SUPER POWERS
collection. (The others will come in waves announced prior to Comic Con).

Is he right? We’ll find out next April.