Pixracer with RTK and a new long range radio

I’m not sure if this is the right category to ask this question, but I was told on rcgroups that I should post it somewhere on this forum.
I’m going to try to couple Pixracer with my another board to bring ultra long range radio + GPS at 1-5 cm accuracy level to UAVs in affordable price. .
In short, we(me+friends) are going to manufacure Pixracer (as its’ open hardware) and wire its GPS port to our board which serves NMEA computed by RTK.
We will also try to put forward a radio made by us from scratch that could achieve long distances with very low power requirements. We have a few years of experience in antenna to circuit matching in this area.
I have a couple of questions, if u do not mind, please share your thoughts.
Do you think this kind of product may be interesting to some wider audience?
There is a discussion on rcgroups about internal magnetometers that do not work properly on Pixracer.
I came to a conclusion that we can modify Pixracer slightly and provide second external magnetometer in the place of internal one. Meaning, we do not solder internal mag. but put a socket to connect an external one.
What do u think? What is the best/robust/reliable mag. that we could use here?
Why are there 3 magnetometers used? Is there any purpose of this?
We will use NO telemetry on long range radio in first version. Radio will be used to send rtcm3 data to rover only. I know QGround Control is able to transmit rtcm3 in mavlink. Is this feature available on Android client too?
Our goal is to have super easy/portable system. No laptops, just phones/tablets.

RTK is not supported by QGC on Android builds yet.