Id love to be able to choose an instrument and build a map of its pitch drift over time (both stretch tuning and chromatic) and then be able to apply pitch correction to other instruments relative to that map; Kind of a groove template for pitch drift that could be applied via vari audio or a midi modifier.
I find myself tuning very good vocal performances to perfectly tuned midi instruments and I’d love to (on Occasions) work the other way around, either modulating pitch across time to fit the vocals or allowing for a global pitch drift within the range set by an instrument.