I will chime in here as I have first hand knowledge of what FIRST means with this rule. This year, we (REV Robotics) developed 3 different MXP boards.
1) the protoboard
2) the more board
3) the RIOduino
We approached FIRST with each one of these boards and sent them through the approval process. We were told that the first 2 boards (which are both breakouts) did not need to be approved because they considered passive. The third (RIOduino) would need to be approved as it is an active device. Just because the intent of it is to be connected to sensors, arduino shields, and LED's because it has the potential to drive motors they wanted to look at it.
The outcome of of that approval process is up to FIRST to release, and while we are hopeful in the results, until they say something about legality we won't know.
We have produced RIOduino's and they will be shipping next week to people who are interested in them, hopefully with a full FIRST endorsement.
You can check out the info for the RIOduino on our site here
http://www.revrobotics.com/product/rioduino/
*on a personal note, I like your take on the board. We discussed many of the additions that you implemented, but decided against them because we wanted to maintain the standard arduino footprint. We see some major advantages of tapping into the arduino platform for FRC, specifically the many shield (LCD, sensors, LED drivers) and code examples which are out there.