I think the next paradigm shift in software is going to be LLM-inferred user intent. Serving just what you really want, when you want it. Currently all inside whatever interface the LLM provider offers, but soon whatever interface the LLM decides is appropriate. People won't use apps anymore. Your LLM will tell you which emails you need to address, and will automatically triage the rest (and action those which can be actioned autonomously). You won't navigate to Facebook. You'll ask your LLMs what your friends are up to. You won't navigate to TikTok. You'll ask the LLM for some funny videos (or whatever you're in the mood for). We won't need to structure data hierarchically anymore. Just dump it somewhere, an LLM vectorises it, and it's super easy to retrieve later in whichever domain one needs it.

The internet is about to undergo radical transformation.

This is basically what my take has been after chasing everything else for way too long. Though I've not moved back and Gmail honestly isn't something I can now move back to (and no tracking/etc are not the reason). I just wrote a too long comment and I realise now most of that you've said in your short comment.

Email for me is just a communication tool that the world still uses. Nothing else.

If you want to be tagged and tracked in that way then there is no better platform than Google services for sure.

but, you're going to pay either way (assuming you have a custom domain).