The only way I could see to do it would have been to have 80h as the default, rather than 00, with less than 80 being negative, more than 80 being positive delays. This still is processed line by line, there is no real negative delay, just your default position has changed from zero to the mid point of the line.
I think it’s probably too late to incorporate something like this now anyway, would of had to be done when Delay column was first introduced, and I can see the mid point being default being confusing to some of the less technically minded too. Unfortunately for people who want it, having a script to make 80h the new default will make lots of other things act strange, such as LFO triggers not being on the beat, scripts not working correctly and probably much more. I don’t really see how to bring it into the already existing stream (unless you could somehow tell the column it was behaving negative, and remember what you see on the screen in just a representation of the data, Renoise could still treat it as being played on the line below with a positive delay.
In fact, having an option to have current 0-FF delay, or 0-80-FF delay in Preferences, with the only differences being what you see on screen with the XML remaining the same, may be possible but possibly a pain to code and adding unnecessary CPU cycles as every single note will have to be transcoded from one display method to another (maybe not much difference though…)
This idea of “Renoise can not handle negative delays” is also destructive to the very good idea of sample cue points, where you set a point where you sample will have played to where you enter the note but it will actually start at an earlier point, as has been suggested again within last couple of days in this thread Note Align (Sample Hit Point) at the end of the day it’s all about how data is shown on the screen, having a sample played 3 lines at 77delay segments earlier than you see the note can not take Renoise more processing to adjust the visual representation than enabling Autoseek on a sample does!