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.
The relevant apps are YouTube, TikTok, Instagram, etc. And they don’t have PWAs as far as I know.
I’d argue it’s even today, simply because apps (and not web pages) are so entrenched. And without apps, a phone is almost useless.
They all have functional mobile sites though, and those can be wrapped into an app-like experience on the client side easily enough.
I basically did that with Facebook back when I still used it. The official app was so outrageously shitty, so I used third-party apps that wrapped the mobile site.
It wouldn’t be great but it’d be good enough for early adopters (mostly technical users). Enough to make a viable niche perhaps, and grow from there.