Some more arguments for a local-based treading model over a content-based one:

1. The format: (#<DATE URL>) or (@<DATE URL>) both makes sense: # as prefix is for a hashtag like we allredy got with the (#twthash) and @ as prefix denotes that this is mention of a specific post in a feed, and not just the feed in general. Using either can make implementation easier, since most clients already got this kind of filtering.

2. Having something like (#<DATE URL>) will also make mentions via webmetions for twtxt easier to implement, since there is no need for looking up the #twthash. This will also make it possible to make 3th part twt-mentions services.

3. Supporting twt/webmentions will also increase discoverability as a way to know about both replies and feed mentions from feeds that you don’t follow.