I think Lemmy already solved this problem way better than Mastodon has ever done. The flow of wanting to "join Lemmy" to there actually being a join-lemmy site, and then you click join a server and there's a recommended one or two right at the top, with plenty of activity and are run well but not neccisarily the biggest kid on the block. i guess the one big stumbling point is that people might get stuck on joining versus hosting a server- maybe the instance list should be the front page of the site and if you know enough to want more info then you can go deeper, and if not you click the first one and go