But that would just be for one recording device. If you could use multiple devices, perhaps with small POV differences that could be corrected, I would expect no limit in that "lossy" case.

But if you surrounded an event with a sphere of sensors, there is still an upper limit. The number of sensors is a function of sphere radius, and whether they are limited to the surface of the sphere (which is reasonable since tightly packed sensors will, in general, get in the way of other sensors).

A sphere 1km across has a surface are of 4pi1km^2 which is roughly 10^7m^2. If you had 1cm^2 sensors then you get 10^4 sensors per m^2, which means you get 10^11 sensors total. At 11k fps (10^4) that's a total of 10^15 fps.

Note that Planck time is 10^-44 so such an arrangement probably wouldn't help for detecting quantum gravity because you'd run out of matter in the universe before you could construct the sensors.

It is not clear how one would synchronize the cameras on such fine time scales either.

Amount of total photons emitted or hitting the Planck limit, whichever comes first.

POV differences could be eliminated by a simple lens & mirror setup.