Therefore, 'Gmail for Mastodon' would seemingly just swing the pendulum back towards centralization.
Nobody outside a select few want to host their own server. And nobody wants to research which server to join, before they’ve experienced an ounce of product benefit, nor how to back up their data. This was always going to be centralised to a degree. But Gmail/Outlook with some Proton/Fast is distinctly better than Twitter, Musk or no Musk.
email adoption was fast because it was a gamechanger compared to faxes and telegraphs. ISPs offered inboxes, as did universities and offices, years before Hotmail arrived.
Additionally, people got email because they wanted to communicate with friends. People get on social media mostly to escape boredom, not intentionally communicate with stranngers.
And it’s waiting for its AOL and Gmail.