Hmm. We're calling our fish wet pets, then some people, maybe without realizing it, want to keep them in conditions comparable to commercial breeding operations that in themselves are not too far removed from industrial farming of animals intended to live just long enough to fatten up and be processed for McDonalds. Not my business to tell someone else how to keep their fish and that's not my intention. Most of us have kept fish in less than ideal tanks, so my point is a more general philosophical one-- if we care about these fish do we really want to think in terms of the smallest possible tank or use betta bowls the size of teacups as a point of reference?
Speaking for myself, I'd like to see hobbyists get away from "what's the smallest tank" questions in favor of "what's a reasonable minimum". Subtle distinction, maybe, but a different mindset, more in keeping with the real reasons most of are in the hobby.
I know it's an afterthought to this thread. Not meant to argue with anyone. Just something to think about.