In short, this solution from Stripe fills a niche, but it's a very narrow one.
Not too sure about that. Klarna in Europe has a similar system called SOFORT in a lot of countries processing millions of transactions [0]. According to a german article, they processed 2.4 billion euros in 2013 [1]
iDEAL using a similar system (officially provided by banks though) is the most popular payment method in the Netherlands [2].
There is probably a big market for bank transfers with instant confirmation for the merchant. I agree with you though that it is a niche in the US, because credit cards are so common. Expansion in the EU would've probably allowed them to access a bigger potential market.
[0]: https://www.sofort.com/eng-GB/press-releases-sofort-gmbh/pre...
[1]: https://translate.google.de/translate?hl=de&sl=auto&tl=en&u=...
1. Because they make less money on cards and card networks are controlled by pushy American corporations, European banks actively campaign against the use of cards online. So instead of feeling confident in Zero Fraud Liability as they are here, consumers in Europe are scared of getting hacked.
2. In some countries, banks don't even print the card number on the card, so you can't use them online if you want to.
3. Cards do not have rewards, so there's much less incentive to use them, even if they could.
4. As a result, consumers are accustomed to using "bank buttons" which let them log into their bank site to push a payment.
5. But that becomes really complex when you have more than 6 banks in a market, so solutions like SOFORT simplify by creating a centralized bank button.
In short, Americans value rewards and convenience whereas Europeans value security. There have been several ACH-based online payment efforts in the US (eBillMe, Mazooma, Noca, etc.) and all have failed.
At least in the U.S, Stripe's opportunity is moving more of that $7T to ACH, not moving existing ACH to their platform.
This is poignantly addressed by @PC's comment addressing whether or not this would be available with Stripe Checkout.
ACH, for now, is generally terrible in retail situations. NO one wants to wait an additional 2-3 days (to all for funds to clear) to see their shipment be sent from Amazon. There are some niche use cases where it may work for pay-ins, for example online custom wood shops—where there's a built in delay to build the product—or other services where physical products don't need to change hands.