It is not easy per-se, and yes it is used in many dissertations, but most of the limitations up to now have been more related to the performance required to implement a demodulator that runs at high enough frequencies in a low cost microcontroller or FPGA. This is becoming less of a problem with more powerful chips. I don't know if I'd call it a mainstream technique, but it is widely used in high performance IPM motor drives for servo applications.

I think this technique isn't commonly used in lower performance applications because it is an additional cost both in performance (need a more powerful processor) and complexity.

The big problem with high freq injection is that it requires some kind of saliency on the rotor, which means this only works for interior permanent magnet machines and not induction or surface PM machines unless they are specially constructed. I guess I don't know enough about hobby brushless DC machines to know if they are IPM or SPM, but my guess was IPM because they can be cheaper to build for high speed designs and I know hobby BLDCs can spin at 10s of thousands of rpm. Perhaps someone with more hobbyist know-how can chime in.

For this application (robotics) I think the other typical problems with high freq injection are negligible. For example you need a well-defined switching frequency that stays out of the way of your high frequency carrier. Many inverters pull back on switching frequency at high loads in order to lower switching losses, but if you lower the switching frequency too much you won't have enough voltage bandwidth to synthesize the high frequency carrier required for the self-sensing algorithm. I don't think this would be a big deal for robotics applications.