I've seen pluggable button melodeons. Problem here is that to mic a free-reed instrument with buttons on both ends you really need two mics, one at each end, and then the player has to stand very very still. I reckon 5 mics on stage is where you really really start to lose clarity unless you have a huge stage and can put the mics miles from each other. But with rock bands I used to have to put up 7 on drums, 1 for each of two guitar cabs, and 3 vox so that made 12, but the guitar mics were down low so they were not too much of a problem. But you got the guitars on the drum mics, and everything on the vocal mics. Using gates helps, but then you are into extra cost and complexity.

Whistles and recorders are sods to mic well too, because of wind noises and the sound comes out of the whistle block or fipple, not the end and you need an expensive space echo on recorders to get them to ring nicely anyway.

2 threepenny bits sharing one mic will make it almost impossible to separate who is doing what, and you will tend to get one player's left hand and the other's right hand, and with a cardiod mic there will be a tendency for each to slip off the edge of teh pickup pattern. I really don't like the idea.