> Who pays for the costs of private cloud compute, is it free of charge for the iPhone owner (at least until they turn it into a subscription)?

My guess is that this is similar to how iOS upgrades are “free”, how Apple Maps is free, how iMessage is free, how iCloud Mail is free, etc. To a good extent, it’s all paid for by the price paid by the customer for the hardware.

I’d also wager that there will be a paid service/subscription that will get baked into iCloud+ at some point in time (maybe a year from now). This will offer a lot more and Apple will try to attract more customers into its paid services net.