I don’t see why the plugin can’t be ported to Volumio3, if the author wishes 
As long as a plugin do not conflict with core volumio and is developed under the new plugins guidelines (we are making a huge effort to improve quality of plugins submitted) then the tinker option will remain open
That’s the spirit of Volumio: the team works hard to provide state of the art features, but not restricting usage of stuff only behind a paywall