Given that there's systems that have successfully flown doing links from GEO to LEO (e.g. high angular rates again), using several year old conservative technology, it's not so bad.
There's a million little details, of course. Just conduction cooling for fast optical transceivers is going to be annoying in space, for instance.
I don't understand what this means. If you mean Facebook-- Facebook didn't drop billions of dollars in to free space optical comms.
> GEO to LEO is not LEO to LEO
Yes, GEO-to-LEO is worse in every way (assuming the LEO satellites are in the same inclination and have the approximate same orbital period):
* Longer link distances. (More path loss, worse link budgets)
* Higher peak angular rates for pointing.
LEO-to-Earth is mostly worse:
* Shorter link path, but atmospheric dispersion (More path loss, worse link budgets, plus things like multipath).
* Higher peak angular rates for pointing.
* Less demanding pointing precision due to shorter path, though.
The hard part isn't the optical comms in space. The hard part is fitting multiple precision-pointed transceivers into a tiny volume and mass budget.
I'm comparing to LEO to ground, which has a higher rate of angular movement (e.g. harder to point at) than LEO-to-LEO in the same shell, among other things.
I've built systems that point to sub-arcsecond precision at satellites in LEO. It's not quite an off-the-shelf controls problem (e.g. good luck getting a COTS motion controller to hit-a-fast-moving-target-at-a-chosen-time, rather than follow a track and not care about time) but it's not super hard, either.