Could this use a software keyboard? If so, it could eventually be incorporated into phones; I'm thinking of a SOC that takes complete control of the screen, bus, etc...
Samsung already did this with some ARM core that could get complete control. How do you know you’re not looking at a software emulation of the secure elements display though?
There could be an LED controlled by the secure element that indicates it has control of the hardware.
It’s a matter of training the user to look for that though.