MobileSafari has an interesting feature that your idea reminded me of: it tries to detect when a site using the Fullscreen API presents an iOS keyboard-lookalik

MobileSafari has an interesting feature that your idea reminded me of: it tries to detect when a site using the Fullscreen API presents an iOS keyboard-lookalike through the location and frequency of your taps on that side of the screen. I’ve gotten the warning when doing something else and was impressed they thought of it.