I already built a first prototype of the hardware and software. With it, you can deploy a fully functional network with as many users, groups, nodes/antenas, etc as you like.
However, there is still a lot of work to be done.
From the hardware part, the most important thing is the power of the BTS. 20mW (14dBm) is enough for deploying a small home network but not enough for larger ones. I expect to put something between 500mW and 1W for a future revision.
Also, a TCP-IP support in the BTS boards is something desirable so the BTS and BSC can be integrated in a single board and there is no need of using a Raspberry PI.
From the software point of view, the next feature I would like to add is anticollision support to avoid collisions between close BTS.