The best thing about PeerTube is that tags on a video are automatically converted into Mastodon-appropriate tags (spaces removed, basically) that show up in search there, it's a really cool feature that definitely helps a lot with discoverability. So this definitely has potential.
Unfortunately on the Mastodon side, you're still seeing a link to the Lemmy post rather than being able to read it in your feed, which confuses a lot of people in my experience as they don't realise they can reply in Mastodon since it looks like a whole separate thing.
So yeah, great work and I think it probably will help some communities, but nobody get your hopes up too much as the way things federate in that direction is just inherently bad at the moment.
p.s. followed the bot on sunny.garden and mastodon.gamedev.place to get things moving ๐
More for other mods to be aware that it's not going to work quite as smoothly as they might hope. But yeah adding that to the bot replies makes a lot of sense, good thinking!
I'm wondering, is it all or nothing in terms of which posts get tagged? For example I mod !knitting@lemmy.world and most of our posts are someone showing off a project, which is easy to comment on from Mastodon (I've been boosting and replying to stuff manually to draw attention there as you described in your OP). But then we also have things like Work-In-Progress Wednesday, where multiple people are posting images of their WIPs to one thread. This doesn't work so well with Mastodon because images don't federate (in either direction) with the exception of the first image attached to the main post, so there's no point sharing it there.
Not to give you more work but maybe it's an idea to have an opt-out keyword that can be included in a post, and the bot will know to ignore that one?
Again, really is great work, you're always contributing useful stuff to the Fediverse and I for one really appreciate it so please take these rambling thoughts in the constructive manner they're intended, they are definitely not complaints ๐