If lemmy created a community the same name as the username when someone signs up. You could follow a lemmy user and then when your on mastodon (once we’re federated with mastodon) you could see their self posts in their community as a mastodon post and vice versa.
Why wouldn’t they federate with mastodon? Its the most used and the simplest UX that could work across different federated software?
Is there some downside to the different projects federating with one another?