Update: It looks like Snipcart is a dead horse. They were bought by Duda and are so busy integrating Snipcart’s features into Duda and facing “serious bandwidth and prioritization challenges”, they hardly even answer support questions or visit their own forum anymore. They’ve more or less gone AWOL for at least six months, to a point where their paying customers are getting uneasy. (I have only used their test environment, to check what is and isn’t possible.)
So I guess it’s Stripe for me, though I really hate their backend. *sighs* But since Snipcart’s in bed with Duda, I don’t think that any close work with Publii is very likely.