It is possible to disable the submit buttons, but the payment button wouldn’t submit the form. But you are right, that should be an option.
Our rule of thumb with feature requests is: as long as it has to do with the plugin, we will add it. How long it takes depends on how complex of an issue it is and how many people ask for it. We just created the list so, for now, this request is pretty much one of the firsts in line.