I have thought if this too JM, thanks a lot for posting this. I have thought a lot more than this design but the best is what I made and I will tell you why.
The curved surface of your pin touches first the one of the pins that are waiting to be touched. Your curved surface cant slip on the pin (that has a curved surface too). If it cant slip then it will no be able to move right or left even a little and it will not touch the other pin that is waiting.
The other design that I had thought is a surface of the pins (that are waiting to be touched) like a horseshoe. The 2 pins that are like a horseshoe leave a hole between them, something like this:
View attachment 338014
this design would work well but it has 2 issues. The one is that you have to be careful to put the "waiting" pins in the right position on button's tube and the other issue is that you wouldnt be able to clean the inside surfaces on them (where the moving pin will touch them).
Be sure that I had thought of everything to make esterigon the best performer and the most user friendly device ever made