I apologise if I am duplicating a suggestion that has already been made but I only have very limited windows of opportunity at the moment! Thus, I don't really have enough time to check back through all the postings or even just try the search facility.
Would it be possible for the forthcoming program upgrade to incorporate an additional level of puzzle difficulty beyond Very Hard, say Extremely Hard or Exceptionally Hard, the new level to encompass colouring and forcing chains (including XY-wings)?