LineageOS (http://lineageos.org/) has OTA updates with UI: https://1.f.ix.de/scale/geometry/710x500/q75/imgs/71/2/1/3/6...
So your dream has already came true :)
Much more info on wikipedia - https://en.wikipedia.org/wiki/LineageOS
Wow
The website and everything else is still new and very much work in progress. I guess their main focus was getting up the core infrastructure before making a cute website.
The lineage site is pretty garbage. It tells you nothing about it, and had I not been following the Cyanogen news, I'd have no idea what it is. It's literally impossible to figure out what it is from any page of the website.
If you're buying a new device, then yes, certainly you should shop for one that's supported on LineageOS or OmniROM, or whatever. But one of the uses of custom ROMs has been extending the life of older devices, and that ecosystem is very spotty.
What you're describing is similar to the situation with mobile devices, only to a lesser degree. Turns out, making an OS run on hardware is challenging and under-appreciated work, and continuing to gloss over the complexity of it doesn't do solving the problem of open-source OSes any favors.
Since there isn't an inexhaustible well of free labor to throw at other peoples hardware there will always be some hardware that either doesn't work right or doesn't work right out of the box because it requires fix foo that is only available in version bar that is the very latest that hasn't made its way into the stable version yet. If you run a bleeding edge distro you may find that you have the needed version of bar but they broke something else!
The solution is to buy hardware with the OS you intend to run in mind. If you are just curious about whether linux might be useful to you the easiest thing in the world to do is try it out either via live usb or virtual machine. If indeed you would like to run linux and it doesn't work with your existing hardware just buy with Linux in mind when you get your next machine.
Instead of asking whether linux can meet the impossible standard of running flawlessly on any pos you happen to throw at it ask whether there exists a reasonable range of hardware that meets your needs and expectations.
If you approach it that way you will most likely be satisfied.
The exception I regularly hit is raspberry pi, but in that specific case I (a) don't actually expect anything to really "just work" out of the box (the whole point of the platform is to hack around on it) and (b) I'm not trying to use it as my primary development / work / games / day-to-day environment.
Unfortunately, I've got an S6 as my daily user phone, and there is currently no stable version of LineageOS that supports the S6 (as far as I'm aware).
The idea to build an OS for every device simply doesn't scale.
On the other hand it has potential for even more 'closed source'-ness on the handset manufacturer side of Android. And maybe even for other industries, once its market share rises.