I too have been trying to visualize what the universe "looks like", and I think this thread might have cleared some things up for me. I have a few questions to try and confirm my theories though.
1) The universe was completely opaque until ~380,000 years after the BB, at which time, nearly instantly across the universe, recombination happened. Shortly afterwords, photons decoupled from matter and were able to travel freely through the universe. This is the CMB that we can currently see. We see it as a surface of last scattering.
2) There is matter (free electrons/protons etc..) behind the point of last scattering, correct? So every year, we see matter (decoupled photons from the CMB) that is 1 light year more distant from our current location right? --in an ideal situation that ignores expansion of space, any time dilation effects etc..-- If true, that means there is a shell of opaque matter "behind" (from our view) this last scattering event that hasn't recombined yet. So even if you move 5Gly away, you can still only see 13.7Gly in any direction because you are just peering farther into the shell in the direction you moved, and less far into the shell in the opposite direction. This is why changing viewpoints still results in a sphere of visible universe being the same (neglecting travel time, expansion etc..)
3) If this is the case, then couldn't we ignore the cosmological principle for a moment and select a special frame of reference that is much much closer to outside the edge of the "shell" of opaque matter? Wouldn't a person in this special frame see 13.7Gly in one direction (assuming they are there "now"), but see to the edge of where matter resides in the universe in another direction, assuming a flat/infinite universe and a finite amount of matter, even *with* expansion?
Everyone with knowledge on the subject seems extremely reluctant to say yes to the last question. Is it because the expansion of space is higher than the speed of light once you look out far enough? So using the "shell of opaque matter" analogy, *within* the shell, but *outside* the current CMB location from our perspective, space is moving faster than light, so we will *never* get to see the true (if it exists) edge of the universe? And because of this fact, there is no point in discussing an edge of the universe? So the only response to said questions by the extremely reluctant physicists are "since it's impossible to know the physics/properties of said reference frame don't even try to think about it" instead of "yes, it is possible there is a special frame of reference within our universe that would create the viewing conditions you set forth"?
Or is there a much better reason to say no to part 3) of my post that I do not know about? The only caveat I know of currently is if the universe is closed, there would be no "edge" to speak of.