Hi
I modified the built in plugin to work with the new Braintree payment nonce, and added in the code for subscription billing, refunds, cancel recurring etc.
I did this work for a site built using nop 3.5.
I don't think I can just give you this code as it has commercial value to my company, but I'd be happy explore being paid a modest fee for it.
If you're interested, please send me a PM