is there some fact about _all_ projective varieties transitively acted on by quasi-simple algebraic group being partial flag varieties that we haven't been exploiting as much as we should? or something... ??something about coadjoint orbits vs orbits of arbitrary irreps.... ??something about whether there are _other_ partial flag varieties besides the coadjoint one that occur as coadjoint orbits, and whether such have natural contact distributions, and how such distributions might show up in the root system?? ...and so forth... ???....