But you can pick an inertial reference frame such that any given photon has arbitrarily high frequency (and thus energy) due to blueshift.

That applies to anything, not just photons. In any event, I'm not an expert in general relativity, but I think what matters is the energy of an object in its own center-of-mass frame (a.k.a. its mass). (And a single photon, or a collection of photons traveling in the same direction, doesn't even have a center-of-mass frame.) Anyway, elementary particles (including photons) already are point-like so far as we know, so they couldn't possibly collapse any further.