Streaming API for conversation updates (and boost/favourite counts?)
Admin interface to inspect failing/unavailable inboxes
Bunker mode to help temporarily mask users against outside attention
Site setting to add custom CSS without compiling assets
Optimize mastodon:maintenance:purge_removed_accounts to use concurrency
Expose number of replies to a toot in the API
UI to filter public profiles by featured hashtags
Approval mode for registrations to help with spam and give invite-only instances a better registration process
Soft-delete statuses for quicker removal (synchronous)