I'm still not convinced someone couldn't build a better gmail.

The web app is bloated and slow. The ads. The awkward design. Privacy issues. There's a bunch of benefits someone could offer. Fastmail tried but I still think it could be better and not based in Australia where privacy has been eroded.

The barrier to entry for doing categorization, spam detection, search, autosuggestions, and even complex JS frontends is significantly lower than it's ever been. You could even offload some of the above challenges to the client with prepackaged ML models. The spam filtering stuff could even be open sourced and community run like Adblockers. Abuse could still be handled server side.