My own mental model (sigh...) is that these are all roughly related to (if not literal types of) the crossover/cross-polination (sigh...) that manifests in synesthesia.

I think synesthesia is definitionally involuntary, but your statement did make me go search "voluntary synesthesia", though I'm not done reading results yet.

I would guess it's a lot harder to identify people who can electively conjure anything akin to what synesthetes experience. It probably feels less distressing or noteworthy, happens less often, and would be a lot harder to study...