I think it's worth looking at desktops for flashability. You can install any OS on most desktops and there aren't that many issues about it. In my opinion, hardware shouldn't break because of bad software. That would mean that an exploit could not only brick a phone's software, but break the hardware beyond repair. What you mention sounds like bad thermal throttling, it's the CPU's job, not the OS's.

My idea of a fair compromise between manufacturers and customers is:

- Let the customer run any OS will full hardware warranty. If a problem looks like it's caused by software, require the customer to flash back to official software, and provide warranty if the problem persists.

- Bolt down the hardware to restrict use out of specs (no overclocking, no software defined radio, ...)

- Provide an engineering pin. When removed, the phone is out of warranty and you can flash any firmware (you can have OC, SDN, custom SSD firmware, ...)

Google really could show a whole more love for tinkerers. A better OS isn't getting made because it's so difficult to flash on your own device, let alone flash it on thousands of user devices.

Regarding your point about keyboards, I personnaly don't like typing without all my fingers, so what you propose wouldn't suit me. But do you think an addon that bolts to the back would be okay for you?