Nice idea, if it's even feasible in the first place. Pretty much any sound deadening material can address specific acoustical issues, but any material that you use will have different absorptive/reflective properties at different frequencies, and in most cases will be ineffective with the low frequencies.

But, fixing the room acoustics can involve more than just sound deadening. Those acoustic "popcorn" ceilings that were popular in the 60s and 70s are actually very effective at breaking up reflected sound waves and keeping sound from traveling and interacting with one another at full amplitude. As with absorbing surfaces, their effectiveness wanes with low frequencies.

Who knows, maybe someone's already at work on this idea of sound absorbing paint. Materials science is one of the most interesting areas in technology right now, so it's conceivable.