The risk/assumption is that once the lead developer/PM/etc. got their promotion l, they get for doing something "new" this is being dropped for a new project as maintenance brings less points for promotions.

Not less points, zero points.

They're complaining about developing software for Google platforms, not working at Google. The platform will get dropped because it no longer has the opportunity to fuel more L6 promos.

I think the obvious notable exception is Android, which is not going anywhere and which now has a fairly delightful development experience with Kotlin and Compose.

I wouldn't call it delightful, but that is as it is.

Kotlin folks have prevented Java support on purpose, only to be forced to update Java support, as Android slowly started to be frozen in time, thus Kotlin losing one of its selling points, Java compatibility, with everyone on JVM world moving beyond Java 8.

Go check any recent Android conference, and most likely there will be a few talks related to Compose performance and gotchas.