This year I did much of the following three on the list:
4. Northern Trail (New England)
3. Erie Canal
2. Ohio to Erie
I can see why the Erie Canal and OTET are on the list. Both New York and Ohio have done a good job in stitching things together, adding signage and having links with adjacent businesses.
I found the Northern Trail OK but underwhelming and not really in the same category as the other two. If I were to nominate a replacement for this list it would be the sequence of four trails in Wisconsin: 400 Trail, Ellroy-Sparta Trail, La Crosse River Trail and Great River Trail. These can link together in a ~140 mile sequence.
I added a comment in Roland’s YT to also consider the multi-part trail running from Kingston, NY to NYC, via the Walkill Trail, Hudson Valley Trail, Duchess Rail Trail, Maybrook Trail, then the assorted Putnam/North and South County trails into NYC. 110 miles all told. You can ride out of or into the city with maybe a mile of road riding.