I agree, that would be great but could be tricky I think.
What I do now is score in handwriting mode on my iPad, then export as much as I've done to Dropbox (choose your favourite cloud software), then open the score in Notion 6 on Mac OS.
The only caveat for me is that sounds for Notion iOS are way less expensive than sounds for Notion 6. A workable compromise is to use existing VSTI's on your computer, but there will always be a discrepancy in the way the two versions of your score sounds
Recently, I upgraded my Mac Pro running High Sierra 10.13.6 with a multi-touch display (multi-touch driver from touch-base.com). Handwriting in Notion 6 with my Adonit Jot Pro is a bit touch-and-go (pun intended). Whatever features for the Apple Pencil Presonus decides to implement in Notion iOS should be implement also in Notion 6. That would make switching between the two platforms using the cloud, fast, easy and transparent.