The obvious things is a tiny RTOS with enough of an ereader buffer to keep 5 screens (random number - maybe even the full boot). press the button the RTOS boots and flips the page almost instantly, then it boot linux in a VM to add more screens to the buffer, and/or take over the screen. Linux would have to be aware it is running in an RTOS like that so it can take over where you left off in the boot.