This is a good idea. I've been working out a plan to move transaction processing to background processes to help with web throughput. I'd imagine I could solve for this problem at the same time.
I've thought about this, but I wonder what the UX is like.
You always show success? What sort of confirmation does the user get? If the card is declined, how do you notify them later? Would that notification confuse them?
"Thank you for placing order number x. Check your email for confirmation."
Email is somewhat immediate if the gateway was up, somewhat delayed if it was down. Regardless, it then offers order confirmation and shipping info, or it offers a card-declined-try-again flow.
