I'm late, so you probably won't see this (might shoot you an email with this same thought.), but I want to echo a piece of feedback I sent to you last year (and the year before I think):
Faster checkout. And improved trust (somehow).
I hear you folks acquired fast.co which seems to be a step in this direction. Entering card details on every site is problematic. Some customers are still worried about it and prefer to use PayPal. Indeed, when I offer both as an option, and make clear Stripe payments go via Stripe and we don't see details, about 80% of people choose to pay with PayPal.
Stripe Checkout, being on your platform and not our sites, seems to be a step in the right direction. I'd also like to see faster payments. My opinion: checkout takes too long. Sites making people create accounts, go through 4 pages and then enter card is bad.
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I think, honestly, integrating fast.co into Stripe and making it highly encouraged is the future. Go a step further and encourage sites to stop making users create accounts. SSO-style system, perhaps, but easy to integrate. Authentication is a pain for me as a customer on sites - I have too many accounts and it drains a lot of time combined. I really think your company has the power to make a difference to this problem.