There is very small amount of registered accounts in Nostr that it doesn't make any sense for anyone to move there, and theymos won't start using any social media just because of this.
I think that Mastodon has biggest Bitcoin community, but it is still insignificant if we look at big picture, and it just create eco chamber for small circle of people.
Point of any social media related with Bitcointalk would be to reach wider audience and different people, not geeks who already know about Bitcointalk forum.