Although I like looking forward to the next macOS name unveiling and seeing new themed wallpapers, I think operating systems should get a regular stream of small updates for individual features and builtin apps, instead of monolithic yearly releases branded as distinct products.

As for API sets, SDKs and third-party app compatibility, they could still be tied to yearly milestones, e.g. "macOS 2020 January", so there would be no breaking changes for apps which advertise compatibility with that, at least until 2021.

Isn't that kinda what Windows 10 does now?