Here is the response I sent Michael via email
We have two things on our list that we couldn't fit in:
Bluetooth and Micro SD Card slot. Putting parts on both sides of the board is cost prohibitive, can affect quality, and would have required us to go to a 4-layer board, which also would have raised the price and made the design less accessible. We really wanted to hit the $49 mark for the Kickstarter, but at $59 we shoot to break even after fulfillment, fees, taxes, etc - so we had to stop adding things. The nRF24L01 plugs in and is super cheap so it doesn't really take much space or add much cost. Wifi (and good wifi) was more important than bluetooth or a microSD - so that's how we arrived where we did. With so many UARTs (running at 3.3v too) it's super easy to add a cheap bluetooth module.
Thanks for the feedback!