For keyboards - again there is a Palm precedent. Sony put out small qwerty thumboards that attached to PDAs that didn't have a built in keyboard. Sony also had a game board with rocker type switches that also attached. We had both.
Palm had an almost full size keyboard that could dock with any Palm. It folded up as small as the device.
Neither used BT or IR.
It could be done - somehow you will have to catch the mfg. collective ear. Just because it's older tech, doesn't mean it's outdated if there is a real use for it. I'd like a decent keyboard at times, too.