I've already mentioned that cliff izunas should be able to go over rails as they could in past games. I'd prefer if they allowed the Shoho Izuna to still work when next to a cliff edge, but I can see where it would become a little problematic to try and integrate that.
Those are really the only changes I'd like to see to Izunas. Of all the things messed up about Hayabusa, the Izunas are great for the most part.