You aren't limited by space in BIOS and hardware interrupts and can have a GUI and working touchscreen at boot without an OS now?

You can't sell a mobile computer that you can't control in BIOS because it has no input devices.

A touchscreen is a built-in input device.

This is a comment that misses the forest for the trees.

What forest? You still haven't elucidated at all what it is you want to accomplish and why firmware is relevant. It seems like it might have something to do with input devices, but pre-EFI machines weren't any more limited in the range of USB HID devices they supported.