Macos used to not have a yearly schedule. New versions took the time they needed. I think it's actually a better model, it allows engineers the time to test and make sure things work. Having arbitrary deadlines just increases the amount of crunch time which usually increases the amount of bugs. Other than that, I wish that Apple did another Snow Leopard and focused for one year purely on fixing bugs in macos x instea…
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…
Though if quality control is bad, rolling updates means many broken updates spread over the year instead of an optional huge broken update every October. Right now I'm on Mojave, works well enough, and I can wait until next summer to update to Catalina, when hopefully the major bugs have been ironed out.