Now the CPU+GPU+Battery are strong enough to make a new OS compatible with open linux kernel and GTK + QT + JAVA + APK... name it
N800 was a wonderful design with stand up hinges, dual SD card support, rotating Camera, pen input, wonderfull screen for the time, support or GPS and wimax...
Build an ecosystem is not an easy feat, but, maybe, adding some of OS2008 diablo and harmatan features to Android AOSP should be a good initiative.
Well if you're interested in a non-Android GNU/Linux phone then you should look at the Purism Librem 5 and supporting the postmarketOS project.
I agree there's a lot of features from the Maemo phones that are still missing from Android.