For now, I think the majority of bandwidth would be the zillions of iPhone users doing backups and app updates all the time. However, this is definitely a way to pave the path for Apple TV+.

Backups are transient relative to streaming which can continue for hours.

iOS update day must be pretty intense - I assume Apple stagger it?

Yes it can. You buffer uploads at an edge server and then drain them at non-peak times.

Edge nodes don't have to be just caches. Plenty of major sites do compute too.

That’s a sure-fire way of getting dataloss. Wouldn’t it be much easier to just upload the backups from users devices when, idk, at night? iCloud requires your device to be locked, connected to WiFi, and charging, so I imagine that already shifts the traffic to off-peak hours.

Not sure it is still the case. MacOS Server have this function if you set it up your network, it will cache all your backup, App Update, iCloud Files and Photos on your Mac.

Something I wish they do for iOS Time Capsule.