Unfortunately just a large multi-terabyte hard drive and just swap games back and forth between it and the system for those that require the speed of the fast SSD. Your older games wouldn't have to be switched back and forth but all games taking advantage of the Series X Hardware would. This will still make it where you wouldn't have to delete any games and their patches if you have enough storage. I'm hoping for a larger card than the 1 terabyte that will be available and will purchase it. Then just keep a 3 terabyte external drive plugged into a usb for the backwards compatible games and extra new gen games. Moving the new generation games back and forth probably won't occur often, but when I do it will still be a lot faster than having to re-download it and dlc.
edit: I just found an 8TB 3.0 usb for $145. I'll probably upgrade from my old one.
So what you saying is all SSD fast but data degrades over time. Best to back it up on a mechanical drive (or two lol)