Hmmm, true.

Does our understanding of Hawking radiation bake in the possibility of a singularity-free black hole (subject to interior vacuum energy) or the assumption there is a singularity (no interior vacuum energy)?

Does an expanding event horizon contradict the idea of a singularity? ie how does a point of infinite density permit a variable horizon if new mass doesn’t alter the density?

Yes to vacuum energy.

I'm not suggesting that the interior of a black hole is a universe, or that our universe is the interior of a black hole, rather I'm asking about the plausibility of a black hole, given sufficient growth by vacuum energy (if it even happens), could be the source of another "big bang" within the same constantly expanding fabric of spacetime and that any and all universes exist - causally disconnected - within said fabric?

In other words "singularity" -> produce a "big bang" -> black holes emerge -> black holes begin "charging/expanding/building mass/energy" via interior vacuum energy -> any of these black holes at their "peak" energy/mass state ala "singularity" -> produce a "big bang" -> repeat ad infinitum.

My god this looks fantastic.