A great feature would be to allow once-off payments from existing patrons. For me specifically, I do custom requests that are charged over and above the standard subscription, and the only way to do this is for the patron to up their pledge temporarily and put it down again. Things get even more tricky when the patron wants two or more custom stories for the month, as the next increase needs to take into account the previous increase for the money to be charged.
I know Patreon is primarily for ongoing subscriptions, but allowing for once-off payments will reduce the friction for patrons who want custom requests.
This is my first post, and glad to be part of the community