You can use celestial bodies for navigation. Eos, moons and the belt. So even without built-in coordinates, it will be easy to calculate your position with simple Yolol code and 3 turrets.
My guess is that common agreement will be:
Starting stations will be 0,0,0
Line from starting station to Eos will be X-axis,
Line perpendicular to the belt an X-axis will be Z-axis, with positive values towards more sunny side of the belt.
Line perpendicular to X and Z axis will be Y-axis, with positive values towards left.
+ maybe some more precise local coordinates in areas of denser population (megastations, moons). Those can be done with transmitter/receiver nav.