A lot of older PC games can run just fine on modern phone hardware. I’d buy a SteamOS version of a phone that has some modular or built-in set of buttons and analog sticks. I don’t know how the app ecosystem would work for sensitive things like banking but it’s mostly a minor issue for me.
I would want to try one, especially if it’s fully compatible between Linux and the mobile modem. Wouldn’t need any controller hardware on the phone itself, just needs a companion clip on controller that integrates nicely. Would definitely try to buy one if it had an underclocked/power limited laptop processor, that switches to full power when connected to a dock or charger. Something that could drive dual 1080p monitors.