Sorry, this isn’t helpful. I migrated the hard way, hah. I just went to each page in OneNote and hit ctrl+a, copied that and pasted without formatting into TriliumNext, then fixed the formatting.
It took some time, but was worth it to me. I figured it would be a good test to help me familiarize myself with TriliumNext a little.
An easier path to help adoption would probably go a long way, but it also might eat up a lot of development time and routinely need work. I’m not sure how often the OneNote export formats change.