The great part about iPad's new windowing model is that you can't hide from it if you're a developer. Users are going to window your apps, layouts are going to be resized, and your menu bar is going to be investigated.
The menu bar API, which is shared with Catalyst, should be your first port of call, as it's something that apps shipping today, built with the older SDKs, now show in the OS. There are plenty of iPad apps that never filled out their menu bar, and you can/should fix that right now
