There is no reason to reinvent an OS. You can use desktop GNU/Linux on modern phones. You only need to tweak the UI (see Phosh). You will also have full computer in your pocket and ability to connect it to a screen and use all Linux apps.
>A mobile OS is much more usable on a smartphone than a desktop one.
The point is that there should be no difference between "mobile" and "desktop". Mobile devices are capable of (almost) everything desktop does. Just connect a screen with keyboard and you have a "desktop". Now, you have thousands of apps already written for GNU/Linux.
What matters is the interface and UI, and the power usage. The android SDK is designed so that app developers have constraints that reduce power usage.
I agree that users should have more power over their hardware, but it would be at the risk of non power users letting malware infecting their device.
But I really disagree that desktop and mobile are similar.
Saving energy on a lithium battery requires more than just better batteries, it also requires developers to make apps that are very lightweight in energy, and that's why android is how it is, to prevent developers to release apps that drains battery and ruins the android experience and the brand.
And what would be the point of having linux apps on a mobile device? That doesn't really matters for users, it's the same problem with linux desktop and the quality of FOSS. What matters is having an OS where users can do what they want, but it's more complicated on android because... batteries.
Also, security is though problem that is solved with the google play service. Yes, it's centralized and users cannot do what they want, but the upside is security.
Tell that to Termux: https://news.ycombinator.com/item?id=25644964.
> reinventing a whole mobile OS
There is no reason to reinvent an OS. You can use desktop GNU/Linux on modern phones. You only need to tweak the UI (see Phosh). You will also have full computer in your pocket and ability to connect it to a screen and use all Linux apps.