How many projects has Trezor included in this fashion? I had no idea!
I like the sound of how fast their out-sourcing is, but could it end up with more room for errors?
XEM is the most recent one which was entirely developed by one non Trezor guy. I don't know about others.
There's no way Trezor would add something to their firmware that wasn't 100% ready to roll. It took a few months from the start to the finish to implement.
As of right now Ledger have more coins on their platform but I presume that's because most of them are cut and paste jobs or clones like Dash and Pivx and don't require much extra work.