I believe 3/4 is about the smallest Mini parts you would want and still maintain playability and
comfort. (which I believe is the shown in the golden t pics buttons)
Ive mentioned this idea before actually.
Even for standup cabs or fullsize control panels.. one could decide on smaller buttons
to add more space.
Also, mini buttons would be nice for Start, coin, and other admin buttons.
However, feel & response is important.. and unless someone is going to spend ooogles of money
on plastic moldings... the resulting buttons out there may not be acceptable.
You could however also make your own mini buttons by carving some wood or plastics.