Suggestion: Blocks layering
The Blocks feature is quite nice in reducing the copy and paste orgies when changing some of your notes. But the experience could be even better if it was possible to set another block as "parent" to the block you're working on, so that the contents of this parent block are put into the child block as a backing track.
That way you could make a "main beat" block and derive most other parts of the song from this one. Then if you later alter the "main beat" block all of its child blocks would be updated automatically.
Interface implementation could be done quite easy: Add a "master/parent block" dropdown on the block edit screen (close to the selector of the current block).
This would even further reduce copy and paste madness and give more room to quickly experiment with new basslines, synths or drums.