With #2, my problem was that without the ability to block categories, different instances would need to use the same shared id for the nsfw tag to let users block all nsfw at once; which is a regression from the current sceme.

general tags are additional to tags above to specify content type

So like hastags? I had assumed 1 tag per post

5. Proposition is for different architecture

Put that in there in case someone asks why I'm criticizing the current plan without providing an alternate one.

Anyways, this scheme doesn't solve what op has asked for, which is to block porn posts platform wide without blocking all nsfw posts. With this scheme they'd need to add every community / instance's porn tag to their blacklist one by one, and it's not even guaranteed that posters would use the porn tag in addition to a more specific tag. Letting moderators set default tags for communities could solve the second problem. But to solve the first one either tags need to be blockable by name (instead of id) or there needs to be a seperate tag category for porn