If not already done, I am wondering if Meraki can develop, as part of it's cloud based product line, another device to connect on the Wireless network that will generate vouchers/tickets with username/password for customers. This will be deployed together with MR devices on the same network for Billing Wifi customers.
Hmm that would be an interesting project. I guess you'd only need a Raspberry pi coupled to a label printer, a screen, keyboard and mouse. Or maybe a tablet and an app linked to said label printer.
This has a lot of "grey", and their are existing solutions already. There is pre-paid billing, were you can pre-print vouchers for customers to use:
Splash Access also have several options.
This really doesn't need to be done in hardware, it can be done in software. It is done in software on some other platforms.
I can't see "rolling your own" as difficult project, for those so inclined. Frankly, I find ticketing for WiFi use abhorrent, and will not use it. I manage to travel widely without using ticket-based WiFi services.