I feel like it should be feasible to add a motor that gives tactile feedback by resisting turning by a little bit (e.g. for discrete power/volume level values within the allowed range) or a lotta bit (e.g. for the boundaries of said range).

Re: multi-functional sliders, I do know that motorized sliders exist in the pro audio space (e.g. to be able to program presets on mixers and such); shouldn't be too hard to adapt them to multiple functions (probably with some sort of indicator on or adjacent to the slider to show the function being manipulated).