[reggoboy]

multiple versions of a song under one entry ... a concept of "roles" where you will be able to assign songs to a specific role (most likely set to each instrument)

This sounds very cool and useful. Maybe perfect.

One note: most of my players don't use MobileSheets, so they won't have any "role" defined in their software. I just send everyone a bunch of PDFs, which is fine for now. But what I'm looking for is a way for me to manage things on my end more efficiently: bundling song "versions" together. 

It sounds like your feature will provide for that, but it's hard to tell what it's going to look like. Sounds exciting either way!