Haha, oh, for a second there I thought you meant tables. But leaving the below..
How about dozens per account? :) I didn’t ship this, but I work for Automattic and WordPress.com is basically highly modified WordPress MU. This means every time you spin up a site (free or otherwise) a bunch of tables are generated just for that site. There’s at least hundreds of millions of tables. Migrating schema changes isn’t something I personally deal with, but it’s all meticulously maintained. It’s nothing special on the surface.
You can look up how WordPress MU maintains schema versions and migrations and get an idea of how it works if you’re really curious. If you don’t have homogeneous migrations, it might get pretty dicey, so I’d recommend not doing that.
How about dozens per account? :) I didn’t ship this, but I work for Automattic and WordPress.com is basically highly modified WordPress MU. This means every time you spin up a site (free or otherwise) a bunch of tables are generated just for that site. There’s at least hundreds of millions of tables. Migrating schema changes isn’t something I personally deal with, but it’s all meticulously maintained. It’s nothing special on the surface.
You can look up how WordPress MU maintains schema versions and migrations and get an idea of how it works if you’re really curious. If you don’t have homogeneous migrations, it might get pretty dicey, so I’d recommend not doing that.