Does something like this exist? As far as I can tell, setting something similar up would require:
- A dedicated Lemmy instance for Mastodon tag-based crossposting (probably, since most existing instances probably don’t want to clutter their instance with thousands of script-generated communities)
- Some kind of form on a site where users who want to follow a Mastodon tag that is not already set up as a Lemmy community could submit the tag they want added, which would automatically set up:
- A Lemmy community for that tag on the aforementioned instance, and
- A Mastodon hashtag bot that automatically crossposts all posts with that tag to the linked community
Yes, but we’re talking about a bot doing this according to the hashtags in the post. The original post, having never been posted to a lemmy community as you describe, can never be interacted with by lemmy users even if a link or cross post is made.