I am picking up the development of this extension, or at least my own version of it. Intended workflow will be the same as what was proposed here. I am looking into whether a business PayPal account would be required to automatically check payment status through the PayPal SDK, or whether we should go with something like Braintree or even limit it all to Stripe.
Idea is to create a new user group for subscribers and only give them access to defined premium tagged content. With a dashboard to set up which tags are premium, API keys for payments, as well as an overview for managing subscribed users and checking payment history etc.
If a user that is not subscribed tries to access a page that is restricted, you will be able to provide a page to automatically redirect them to that describes plan information. Possibly integrating with the Pages extension.
Once I have a singer tier subscription model in place I'll work on creating admin configurable permissions for multiple tiers which will just be glorified user groups, and allow you to set which tags are available to which groups. I hate to see this started from scratch again, so if anyone has already made decent progress with this and wants to see it continue I'd be happy to lend a hand. I can usually be found on flarums discord as well.
