I think limiting/silencing is an excellent solution. It gives the people who want to interact with Threads a chance, while not disturbing the people who don’t.
In regards to Lemmy: I’ve seen a few Mastodon users tag Lemmy communities and creating posts here (generating some hilariously broken Markdown titles in the process), so we may see a few posts here or there. I don’t think anyone over at Threads knows what the Threadiverse is, though, so it shouldn’t cause any problems.