This is the first step towards the "marketplace" feature of WePay or PayPal, which is great. But it's not very useful unless I can add a fee for myself.

On a $100 purchase, I should be able to split the money so that $3.20 goes to Stripe, $1.00 goes to me, and $95.80 goes to the seller. Without that ability, I have to make up a separate billing arrangement with the seller, either a flat rate (eg subscription) or calculating fees and billing them post-hoc - messy and unreliable.