I hope the big ones adopt this even for replies to kind 1. Huge data savings for root only feeds.
This is an interesting new spec that will allow you to make threaded replies to pretty much anything: geographical areas, websites, hashtags/topics, urls, podcasts, books, movies, papers.
https://github.com/nostr-protocol/nips/pull/1233
right now you can really only make threaded replies to kind1 notes and trying to do it on other things is kind of janky. generic comments fixes this.
Discussion
It would be a terrible breaking change. Less active clients would have their user wonder where all the people went as nobody would reply to them anymore.
To fix this I suggest to add some "level" to kind-1 events. Root events should have a tag "l", "0" with replies omitting this or better yet setting the distance to the root so you can query all first level replies easily, too.
I realize this would lead to modern clients having to set but not use l-tags in queries until wide adoption was achieved. Else they would not see legacy client root events.