I kind of doubt that support is dropped due to difficulty in development at this point, it's pretty much planned obsolescence with a weakly credible excuse, the only thing that can truly work would be having a common AOSP image that you can switch to whenever you want, since that's vendor neutral you wouldn't have to wait for your phone maker to create their useless customization of the latest version of Android.

How I wish Android had been copyleft, maybe everybody would have concentrated development effort on a single platform then, instead of making awful skins with bloat, sponsored apps, etc. with extra features on top that should have really been contributed to mainline