Although inversion, retrograde and retrograde-inversion are three *major permutations of an original melodic fragment which some strict serialists insist as the only ones available (in 'pure' form, of course) ... I'm sure, by now, you'd be able to guess what I think about that *ideal. However, those are only one of many tools to use in an infinite number of constructs, of which your description has just begun to suppose.

...reasonable continuity... I wouldn't go that far.

...notes stacked up on each other......and as I'm sure you have summated, this takes what would *normally be melodic into the realm of harmony (farbeit from me to mix the two).

Anyway, in a previous post one of my intents were to "repopularize" retrograde as a verb. I'm summizing my own failure...