Well for polyphony the "which note goes where" issue could, with creative sequencing, be solved by using different channels for each individual note to override

Well for polyphony the "which note goes where" issue could, with creative sequencing, be solved by using different channels for each individual note to override the synthesizer's configured behavior [also enabling the use of simple pitch bends for the effect] - but I guess any good solution here will end up requiring even more hardware or software to allow this [it looks like this is essentially the goal of MPE] and, as you imply, arguably be a "nonstandard hack". But music IMHO is often about finding value and personal expression in the nonstandard along with the standard (perhaps I'm a little biased from too much jazz, because admittedly this isn't the case for all players in all styles). And musicians have certainly employed MIDI to use these techniques for decades. Regardless of my possibly misguided attempts at defending a 36-year-old spec, I absolutely still agree with you, however, that an improved standard could certainly make having more creative control simpler and easier, requiring fewer "hacks".