I suggest to change the existing ones, since horizontal planks make no sense for vertical poles which make up the majority of the block (and uses)
Sounds reasonable to me. Fences in vanilla MC 1.0 lazily re-used the vanilla wood texture. The creator of Dokucraft did not think to change that behaviour and so about 8 years later, here we are, still doing it that way.
It's a long-overdue fix in my eyes, and one that I'm happy to commit to.
While I'm at it, should I overhaul the fences with vines and leaves on em too? Not promising anything but it may be possible to use the most recent Optifine Overlay magic to give these biome dependent colors like the leaf blocks at the very least.
Also how about some new fence block models?
https://www.youtube.com/watch?v=9uy4zpnuZmY @2:40 and more at @12:00