Love the concept. There are a lot of "you should do X" comments in this thread, but generally speaking this is a great design as-is.
Say your robot comes in at 150 lbs (w/ bumper/battery), and the game is similar to 2012 where typical strategies go about 20 feet in a single sprint. In other words, you've determined you
need a 2nd stage for that game. 2015, 2014, 2013, and some 2016 bots wouldn't need a 2nd stage at all, so this is pretty situational.
Since this gearbox is modular, a new gearbox with the same interface should be plausible. How would you re-design the gearbox to do it?
edit: for reference, you'll want to go
way back in JVN's spreadsheet history:
https://www.chiefdelphi.com/media/papers/2750