Assuming that there ever will be another version and NotesPlus isn’t as dead as the level of support would suggest, I would first of all be with everyone else in saying fix the major problems before even thinking about new features.
If you do reach the stage of having a fairly clean product again, then my request would be an option to turn on a horizontal ruler, either in the full-page view or in the magnify window or both. When in the magnify window, the measurements shown should be still the measurements from the full-size window (ie. if the magnify window is showing a part of the page on the right hand side, then the ruler may show from 11cm to 20cm or similar).
I guess you’ll need metric and imperial options, probably pixels as well.
For me this will be really useful when I’m in the magnify window but want to keep things lined up on the page. For example, I can do my bullets at 1cm increments.