Legislating such a micropayments system would centralize the monetization of internet services in a way unprecedented since the advent of the internet. If you're worried a lack of Net Neutrality would suppress free speech, this would strangle it.
You'd create two internets: a bourgeoisie sphere of corporate sites with enough influence to be included in the micropayment system, and the unwashed masses, the sites deemed unworthy of monetization, forced to survive on crippled ad market. The handful of large corporate microtransaction payment processors would get to pick and choose who gets to be on the "good internet" without any oversight.
Who said anything about legislation? There's no need for legislation around this.
The problems so far with micropayments infra is that publications don't believe their readers will prefer payment over ads. Which is unfortunately largely true, so anyone starting a micropayments company will have a lot of trouble developing the network effects (both on payer and payee side) to be successful.
I don't know the solution to this, but I'd hope it's not legislation. Well -- a possible solution might be legislation that makes it economically infeasible to run sites on ad revenue and selling data. If we make it onerous or impossible to allow sites to collect and sell data, and make it harder for ad networks to target people, sites will have little choice but to implement subscription schemes, or, hopefully, adopt a micropayments-type structure.
You'd create two internets: a bourgeoisie sphere of corporate sites with enough influence to be included in the micropayment system, and the unwashed masses, the sites deemed unworthy of monetization, forced to survive on crippled ad market. The handful of large corporate microtransaction payment processors would get to pick and choose who gets to be on the "good internet" without any oversight.