TMNT director Kevin Eastman revealed, "Although the CGI film did well enough to warrant a sequel, there has been much talk between Imagi and Warners to do a better 're-invention' (newest Hollywood buzzword) of the TMNT's, in a live action film -- like what was done with Batman. Back to basics, back to the origin and the intro of the Shredder, etc." Eastman added that "there have been talks, trips to Northampton to talk to Mr Laird, and discussions with the original 'first' TMNT film director Steve Barron to come back and do it right -- but no official word yet."
So the TMNT movie was a hit (but not as much as the original Live-Action film), but they want to a Live-Action film instead of CGI, but it is not because of budget reasons but its because they want another Dark Knight! I don't know if Laird and the movie company will agree on something, but they think they want to go back to the comic book roots, much like the second cartoon. The comic book was pretty dark, much like Dark Knight, can they do it?
IGN: TMNT Sequel Update