Well, I just hauled out my old Nook HD and discovered, lo and behold,
I can put Cyanogenmod Marshmallow on it.
Only 10% of Android devices are running Marshmallow now—and one of them is my 2012 Nook HD. It's a bit slow to launch some apps, but it runs e-readers just fine, and even streams movies. I had to use an app downloader to grab the APKs for the Nook app and Hulu, which Google Play didn't think were worthy to grace this decrepit hardware, but they ran just fine when installed.
Pretty crazy, huh? Potentially more along the lines of demonstrating just how many clowns I can stuff into one car than actually
useful, but you never know.