There's an option to combine NHF and part of NCF.
-NCF is quite large in size, unlike NHF.
-NCF is unbalanced. I wouldn't want a creature from NCF to appear on my guard post, while my opponent has a creature from the original game on the same guard post! However, the problem of yellow druids already exists in the original game, but this would happen much more often.
However, I see a solution: NCF mainly serves for offline games (at least offline players love it the most), so you could release a special version of NHF for offline play, making it compatible with NCF, including heroes that use creatures from NCF, and adding heroes with combat scripts. I think that would be a good addition.
P.S. But guys, let's discuss NCF in the NCF topic, there's no need to mix things up ;)