I am currently faking the button by using a toggle with ofParameter and a listener function that also sets the parameter to false, but that's not really cool.
I also like the feature to let the event that gets triggered by a button be part of a parameter group. I would still vote for ofParameter>. The parameter thing would make sense if you could have a button that also triggers another button if you make a reference from one parameter to the other..? Or how would that work?