I don't see deprecating fstab as a bad thing, if it's possible. Less static configuration is pretty much universally good. It's also pretty much zero burden on systemd to maintain fstab compatibility indefinitely.

However, I was asking for specifics. Accomplished how, exactly?

udev can generate an event and run a shellscript or something when devices become available, but... then what? What processes the event and ensures correct behaviour for dependent services?