The neptunium hoe cannot hoe/till the rich soil from Farmer's Delight and also therefore cannot be used to keep soil permanently moistursied.

Rich Soil is already a farmland. Hoes only turn dirt/dirt variations into a custom farmland, that's permanently moisturised.

We (Or Farmers Delight I guess) would have to add a custom Rich Soil block, which stays permanently moisturised, which is not something we're looking to do.