Awesome! I'd love to hear more about the ideas and how I can implement this best to help. If you have the time, my e-mail is in my profile :)

Oh interesting! Thanks for the link - will definitely be following that, I think it's a really good idea. My one fear is that some websites will try to trick users with dark patterns that their purchase is 1 time but will actually be a recurring subscription, but I'm sure if wallet confirmations make subscriptions clear that should be less of an issue.

Yes you can. You could create an smart contract where you lock X amount of eth, and set up how much the other party can withdraw each month. Then is up to the provider of the service to withdraw the amount each month, which seems to me less an issue since they want to get paid.

Yep, but as the other commentator pointed out, you need to take all the ether at once. So if you wanted to charge 0.1 ETH a month for 6 months, you would need to take 0.6 ETH up front into the contract, which kind of defeats the whole point of the subscription model.

The smart contract could allow the user to withdraw the unused ETH to cancel the subscription but the fact that it still requires the entire amount upfront makes it an extremely poor user experience.