(As an aside, Stripe prices bitcoin payments at 0.5% rather than 3%.)
I don't follow your description of Case 1. On Dec 18, to use the timing from your example, you have two options: (a) keep the $380 object (b) exchange it (via a refund) for $380 worth of bitcoin. These are the same options that you would have if Stripe was not in the picture: keep your funds outside of bitcoin or buy bitcoin at the market price. I don't see what benefit you derive from the refund API (beyond using it as a fairly priced bitcoin/USD exchange). Sorry if I am misreading the example!
I don't follow your description of Case 1. On Dec 18, to use the timing from your example, you have two options: (a) keep the $380 object (b) exchange it (via a refund) for $380 worth of bitcoin. These are the same options that you would have if Stripe was not in the picture: keep your funds outside of bitcoin or buy bitcoin at the market price. I don't see what benefit you derive from the refund API (beyond using it as a fairly priced bitcoin/USD exchange). Sorry if I am misreading the example!