Why not stick with AX.25 and packet radio instead of reinventing the wheel?
I don't know why but there doesn't really seem to be a push to so better on FM digital modes compared to what you see with FT-8.
It feels like outdated tech to me, all the hardware is generally big, slow, power hungry, and expensive.
The APRS system also has issues with timing and flooding a channel if there are too many stations in one area.
Seems pretty common to put similar bare boards in people playing with high altitude balloons.
Sure APRS has limits, but keep in mind that you don't have to use the "APRS" frequencies, for high density uses like say a bike/horse/foot race it's pretty common for support teams to have APRS to help coordinate and to use a non-standard frequency.
So tracking 1000s of devices second by second, sure that's not going to work well.