Material 3 is mostly not part of the AOSP tree (aside from some very, very deep code like shadows) and is just UI libraries. I actually wonder if M3 has View implementations, or if everything has been migrated to Compose.

You're also underestimating the amount of fundamental work that goes in Android. The vast majority is hardware integration. It's not all fancy little bells and whistles. It would have the added benefit of not having to relearn the security mistakes like LIST_ALL_PACKAGES or READ_SMS permissions being open to all, at least.