For those of us who don't have a surplus of keys, I would love to have the option to pay crowns to farm key bosses. The keys are very rare drops and they shouldn't be. There could be something at the sigl giving the option of using a key or paying a certain amount of crowns. Or you can sell packs of keys and only keys in them. Would love to see this implemented.
How about being able to craft them? I don't think everything needs to be easily handed to you with $$.
Personally I am tired of crafting. I am also tired of incessant farming. Crafting usually involves rare reagents you have to incessantly farm for or difficult to catch fish. Just tired of it. Really, who loves doing that? Gimme a slot to insert crowns in and I am good to go.