Max cost for payment
There are already plenty of options we can set, but there is one that's missing.
Say you want to have a percentage cost of 2.5% for PayPal payments.
But you don't want the cost to exceed 5€, setting a maximum cost (and maybe also minimum cost).
That's just adding 2 extra fields on the payment cost configurator and taking them in account during calculation.
Being a developer myself, this is a no brainer and quite easy to implement I think.