One of the problems is that people who paid for Google Play purchases and other services have no way of migrating them to a free Gmail account.
Just set up your MX with some other service if you are not happy with Gmail, or start running your own SMTP server.
Your current G Suite legacy free subscriptions and related services will continue to function as they do today, until you self-upgrade or we upgrade you automatically to one of the new editions."
That "until" is really ambiguous - does that mean services terminate when you self-upgrade?
If you cancel it, your account is converted to an ordinary external domain Google account AFAICT. You need to migrate your email out of Google/Gmail to get service messages over email, but you can continue using your Google account as an ordinary Gmail-like account - only difference being that you handle your email yourself (because you didn't want to pay Google to do it for you.)