Suiramus if you are referring to the JSON:API changes discussed by askvortsov in the mentioned tweet, you don't need to worry about it, it's a developer thing and doesn't even impact how data is stored on the server.
If you're referring to the importer stuff, I don't think it's relevant because you either migrate now, or later, but not both?
If you are referring to the possibility of a future web installer/updater, there will likely be no loss of data.
Flarum uses database migrations to change its database structure between versions. Migrations run via the web upgrade page, which already works on any kind of hosting (as long as execution time/memory via the web isn't too limited).
Updating to a future version that has a built-in updater will likely be exactly as updating to any other previous Flarum version. You will have to move your forum to a host that supports SSH, or re-install Flarum and then point to an existing database. You will likely have to do this multiple time already in the meantime to stay on the latest Flarum version for extension compatibility and security updates.
As Matt said, it's currently not a priority so it might take a while. If managing Flarum without SSH is troublesome, we recommend moving to one of the many hosts that provide SSH.