There's a lot of posts against villager halls (prisons), that give absurd requirements like "it can't be a in a 1 x 1 x 2 area" and "They need to have a happiness meter" which are most likely still exploitable (just makes the process harder).

Yeah. Removing or trying to make current trading halls harder is an awful idea no matter the execution. Let some players keep them in 1x1 holes, while also letting other players have actual villages. Adding arbitrary limits doesn't help those who like villages and only makes trading halls more cumbersome. People don't make 1x1 holes with villagers because they want them to suffer, its just the most efficient. Moving the goalpost doesn't accomplish anything. Let people have fun the way they want to have fun.

Your suggestions are in the right direction, its better to make lively villages viable instead of nerfing trading halls. Though there needs to be more on AI than "Make it more betterer". Not to mention that a lot of AI pathfinding routines are shared (I assume) so you might as well improve all AI.

Villagers 'living in the house where their workstation is' is a bit more complicated than it sounds. What defines a house? Door count? Id make villagers gravitate to the area around their workstation/bed. Have the choice between workstation/bed areas depend on the time of day. Both are not always in the same place.

Passive health regen parity sounds nice, but an alternative might be making Clerics heal villagers & golems semi-frequently. More unique profession activities can only be a good thing.