what you mean would require to set your root scale, or the chords you want to use in advance. Quite complicated.
I think a simple chord detection system is all I mean.
I imagined 2 little buttons beneath the octave button in the Arp section, with each button showing a dropdown menu with Key on the left button (C, D, E, F etc) and a Major/Minor dropdown choice on the right button.
Then the arp pattern could be additionally addressed by a "chord recognition" lookup to fix the 3rds and 7ths, based on the root note played. This covers 90% of tunes.
A number of plug devs have already done this, including for midi sequencers, a lot of kontakt sets, and a very few synths.
It extends the melodic capability of arps considerably.
Anyhow, I know you have lots of great ideas already., and I'm looking forward to them.
As a footnote: Over the years, I've seen midi note editing capabilities are often lowest on any synth dev's priority list. But you're a pretty fine counterpoint musician, so maybe you get it
And great news on midi import