The federation/migration problem in mastodon seems very important. My broader thought: SMTP/NNTP/etc. thrived because of a set of trusted entities (govt/uni) that could reliably run federated servers. My choice of server is going to be based on which one is most likely to be up and running years in the future.
Who should those entities be today?
Agreed. Now if only we had cheap/easy account migration and/or meaningful account linkage of some kind. This would be the only thing likely to motivate me to start an instance.
There would be an attraction to starting one with membership only open to people who've been around my infrastructure coding group a while as a badge of honor thing, plus local feed making it easy for alumni to connect.