I received a heap of feedback. All of it was great. Thank you all so much! After exploring a bunch of options, I've decided to stick with plaintext. I'm going to continue to use nvALT synced through Dropbox on macOS, but purchased a TaskPaper license to use for todo lists, and when I need to re-arrange items in an outline. It is set up as nvALT's default external editor now. On iOS I've settled on using Editorial, and app I've had in my wish list for...probably years, but never purchased. So far I'm pleased with my new system. I had a day filled with meetings today, and was able to move smoothly between macOS at my desk, and iOS in the meeting while taking and reviewing notes.