There have been few, if any, composers featured in Doctor Who, and if they are to be introduced on screen, then the best idea is to start with a famous one (my first idea was Béla Bartók). Bach composed over 1000 works, and is seen as a great composer. Maybe he had writers block one day but then the Doctor arrived and gave him a life-changing break that revolutionised his compositions. There would be some incredible music, and I'm sure many fans of Doctor Who, like me, love a great piece of music - I mean, have you heard of Murray Gold (and Ben Foster)! Yes, he is once again, relatively unknown, but I'm sure there are some great Bach jokes - or you could combine him with Chopin and bring out the old 'Gone Chopin, Bach soon!'. He's also a composer who isn't blind or deaf, not that it would be bad if he was, but that does give you more scope in the episode. I understand that this is one of the rarer possibilities, but who knows, it could happen one day!