I'd like to see support for MOD-style music (MOD, S3M, XM, etc) supported.
For those not familiar with these, check this wikipedia page: http://en.wikipedia.org/wiki/Module_file
It explains it much better than I can.
You could even make it so that each channel can be activated or deactivated by the Contruct-user/programmer, so that you can do things like in super Mario World, where the drums would only play if Mario was riding Yoshi.