For a break-out board I'd like to see most of the 'slow' I/O brought out into a nice format (0.1" being the obvious one).
Most vital is JTAG (why that's buried in an obscure high speed connector is about the only bit of the design I can't quite figure out :-/)
I2C would be nice for debugging and hooking up some little devices
SPDIF for providing basic audio without using the complexity of HDMI packet encoding in the PL
And then a hand full of GPIOs
I'm wanting to use mine in a bare-metal situation, and tbh assumed the JTAG would be easily connectible, only just noticed that's is basically SMD only accessible
So a nice JTAG breakout board will likely be the difference between using and not using ( I'd like to make my own break out board if one doesn't appear but that's not something I've ever done so ... )