Feeds. Creators collect and filter on subject, importance and volume. Follow a Feed instead of a person.
Locality. Connect people in an area, like Facebook starting in schools. Use age and membership (church, work, school) for getting people onto a server where they know people.
Events and Calendar. Instead of posts with date/time information, make a different type. Let people view aggregated calendars with multiple filters, and make Feeds for calendars.
Private chat groups with their own invite and moderation choices. Put keys on mobile devices so the server doesn't know; can't be available on a website client.
Minor suggestions: Make moving accounts dead simple, and with that, have a global registry/dns for names. Change the name "toot"; isn't "tweet" generic at this point? A tagline of "blow your horn" with a mastadon tusk as the horn.
(IANAL, but former tweep)
Mastodon doesn't make anything 10x better or easier. It will never gain mass adoption accordingly. Mainstream users will never care about it, not under any circumstances.
It'll languish as just another techie fantasy, with every other decentralized premise (not one of which has ever acquired mass consumer use, not in decades of trying). It's the standard techie failure to understand average users. The same reason techies for nearly two decades have been baffled as to why average people haven't adopted command-line Linux - they can't be objective and properly put themselves into the shoes of other non-tech people.
You mean like Google, Apple, Facebook, Microsoft, Uber, Youtube, Instagram, Snapchat, Shazam, Grubhub, Bell labs, Intel, Xerox Parc, Pixar, Amazon etc, just to name a few (and of course Twitter)? Techies have been doing just fine in the anticipation department.
I unfollow everyone who becomes overly political or comments on every outrage-du-jour. These people are inviting the bullshit. They're not making important contributions to political discourse. I don't care if they get dogpiled for it.
As a result, my Twitter experience has been smooth.
Even though in many cases, I would otherwise be in complete agreement with the core argument being made. The vitriol and vociferation is vexing though (sorry about that).
For all the shade I throw in its direction, the 'snooze' and 'unfollow' features have been more than welcome additions to Facebook as far as I'm concerned.
Gotta be honest, I never thought I'd see the day where "First day of school" pics and statuses actually get engagement from me--they're so much more pleasant and calming than "($CONSERVATIVE_PERSON| $LIBERAL_PERSON | $GROUP | $PARTY ) DID A THING, I HAVE FEELINGS ABOUT IT, AND YOU'RE GOING TO HEAR ABOUT IT".
This phenomenon is more concisely expressesd as "boo outgroup".
I don't think the advantage for Mastodon is being able to do anything that Twitter can't. Instead, it's being able to do everything that Twitter can without a lot of the negatives that come with Twitter.
My view is that, fundamentally, Twitter is a good platform, but it suffers from a number of toxic elements (dog piles, turning everything into angry politics, new "features" designed to increase engagement/number of ads you see, etc.). I'm guessing that "Twitter, but without everything you hate about Twitter" is enough to overcome the network effects, especially as Twitter keeps finding new ways to annoy its users for money.
But maybe I'm wrong about that. I guess we'll see.