With 1.17 coming soon to be released it would be a good idea to bring back this proof of concept and make it an actual feature than just a proof of concept.

This would allow the use of biome tags, or anything which has a registry for (dimensions tag, etc.) and would be a very welcomed feature.

Nice! If this does get considered, having preset biome tags similar to Forge's API would be very nice.

From what I see now, mojang is now very lenient on these tags' registrations: anyone can call RequiredTagListRegistry.register and add their own required tag list. We still need a patch on RequiredTagListRegistry.getRequiredTags to include those extra tags we register.