I don't know about this... Keys are already in every store (I think) so there isn't a real purpose. On the other hand, it would be nice to purchase them with souls seeing as farming souls are so easy. I think it would be a welcome, yet unneeded change tbh
I'm with qubi, keys are in almost every other store on skyblock and there's really not a point in adding keys to kilton unless they just needed something to fill in the empty spaces. Kilton is mostly more valuable rewards in my opinion like the Mystic Set they have in it, and keys don't necessarily fit into that category. Also, like qubi said, heads are fairly easy to grind and get from /ah or people auctioning stacks off in chat.