The fact that publishers haven't experimented with that implies they're not interested, which dooms any project like this from the start.
• Advertisers want subscribers because that's a proxy for wealth and often, locality.
• Only quite rich people are willing to pay for an ad-free newspaper. The Spectator is one example of such a thing in the UK (subscription only, no ads).
• A lot of subscriptions are driven by a desire for opinion and opinionated takes, often by a single star writer, not news and certainly not neutrally written news.
Extremely slanted opinion sells like hotcakes and subsidizes all the rest, but the market for drive-by micropayments for opinion is very small. This opinion-subscription-bias amongst readers is why Substack works and also the Guardian (the Guardian is 90% just opinion pretending to be unbiased news).
Obviously limits need to be built, otherwise the heavy readers will drain the provider's bank account...
The other issue is that big name publishers saw micropayments as eating into their subscription revenue and weren’t interested, but without them it was hard to put together a compelling enough bundle of sites to overcome the signup friction for users.
I still think it’s a good idea but I don’t see how you overcome those obstacles.