While not practical as keyswitches on an ordinary keyboard, they do have applications. Touch sensitive light switches are widely available:
Touch sensitive light switch
Touch sensitive light switch This particular switch needs an enormous 47mm pattress box, and has extremely irritating dimmer functionality – which prevents it from working with compact fluorescent bulbs – but the switch fuctionality is of fine quality. Such a switch uses a charged surface and capacitance to detect contact. The degree of touch sensitivity in response to finger touches is excellent. It could be nice if this switch technology was available for computer input devices. It can be useful for infrequently-pressed switches. However, there appear to be some issues: – One of these switch use a metal plate. Programmable keywitches with relegendable keycaps tend to have transparent surfaces, which tend not to conduct electricity; – These switches are hooked up to the mains. Sustaining their surface charge takes some power – around 100uA at 240V – and an implementation that pulls power from USB and has greater than a handful of switches may not yet be practical; – In practice, touch-sensitive key switches do not yet seem like widely available.