It's not "officially" supported, but iFixit has a guide for swapping the drive on a time capsule. I used mine with a 4TB drive for years with no trouble.

Sure, but still just a single drive.

My old trusty readynas should still work i think.. probalby. Supports smd for time machine and smb3 generally. If it doesn't I might finally be pushed onto a nas that isn't discontinued.

I had an early ReadyNAS that was a champ for years. I wonder if the fact that it was based on SPARC had anything to do with its longevity.

the one i have is my second readynas.. its a later one and is x86 but it's still kickin'. The first failed suddenly so i bought the second hoping to migrate the disks, but they changed the architecture so that wouldn't work. I determined that all that happened to the first was that the power supply gave up. Sourced one from ebay and it was back to working but i went ahead and did a migration then gave the old one to a friend. It's apparently also still doing just fine.

From a risk assessment standpoint, I’ve seen my Time Machine backups corrupted much more frequently than I’ve experienced drive failure. Happened with both my Time Capsule and then my Synology RAID.

It’s a “nice to have” automatic backup, but not a primary backup destination for me.