The trackpads look great. Hopefully they can deliver on the promise of making mouse and keyboard games more accessible on the tv console.

The Y and B buttons look difficult to press. Given the arc that your thumb travels on pivoting from the base of the controller handles, it may make sense to shift the buttons down and towards the center.

I would also consider removing the on-controller screen. It adds a big per-controller cost. Also, when have these been successful? Neither the Wii U nor the Dreamcast did this idea justice. Was it just bad implementation? I think its just a bad idea.

Treating your program as a black box with set of inputs and outputs to avoid library reliance is useful. As mentioned, it increases portability, eases maintenance and future revision. One downside however might be not taking full advantage of library implementation details for performance concerns. Anyway, this sounds like a case for building for interfaces or abstractions, and the same arguments apply. I would agree though that this is a good approach to take in general.