Harry, thanks for pursuing this topic with Steve Siebert.
What I would be willing to pay $500 for includes some features that I
recognize might be of little interest to others:
1. Ability to read and write files in Nota Bene 3 format (which I
think is the same as XyWrite 3) and to set this ability as the default.
2. Ability to read and write files in .docx format--by which I mean
the ability to serve as a full and accurate front end for MS Word,
including track changes. In other words, better conversion to and
from Word than currently offered in NB 12; the current NB 12 ability
to export as .rtf does not achieve this goal.
3. Full XPL, along with a lucid and comprehensive manual on XPL programming
Best,
James