I feel like this would be a lot more viable today than it was when Ubuntu and Firefox tried it. Progressive Web Apps have come a long way, both in terms of quantity and quality. Newer desktop Linux apps have more flexible designs as well, so they could probably be adapted more easily than back then.
Hardware support in terms of CPUs/SoCs was never the issue. Ubuntu touch ran perfectly on my Nexus 4 in 2014 or so.
But the software is just not there. There’s no app store to speak of and you can hardly buy anything running not Android or iOS off the shelf.
I feel like this would be a lot more viable today than it was when Ubuntu and Firefox tried it. Progressive Web Apps have come a long way, both in terms of quantity and quality. Newer desktop Linux apps have more flexible designs as well, so they could probably be adapted more easily than back then.
Might just make more sense to fork AOSP though.