Having overseen the update of an app to support the new layout I disagree with you. The main issues we found is the virtual home button that could fall in the locations where you have buttons (allegedly is not a problem with built-ins like navbars, but still an issue on some screens).

Another issue we found is support for the overflow when hiding the top bar on scroll and other minor issues that I have no time to tell.

But the real problem is that you need to test and test all screens, something difficult in a complex app. Especially since the X was released in late November and difficult to find for some time.

That does not mean that having a compatible app by April, 6 months later is a hard requirement. But updating the support requires a good amount of work, it is not trivial and could consume a good chunk of time to do that.