Is there a LEGO Rock Band in the works? If we're going to base our answer on the recently-concluded GDC presentation of Harmonix senior designer Dan Teasdale, the answer would be no. However, if we are going to base it on his should-have-been presentation, that's quite a different matter altogether.
A PDF of the designer's earlier version for his design session showed slides that revealed the game in a timeline marked for 2009, sometime between Rock Band Unplugged and The Beatles: Rock Band.
As to why the slides delivered at the actual presentation made no mention of the LEGO Rock Band anywhere at all, we do not really know. Rumors of it being in development under Traveller's Tales have been afloat, though.
The slides also reportedly showed a few other Guitar Hero titles listed, and supposedly lined up for future development (yes, it's definitely not over!), including the more-buzzed about rumor of a Guitar Hero: Van Halen.
We'll wait for official word from either Harmonix or MTV Games - or both will be better - but in the meantime, just stick around for development on this news.