Ryan, geolocation and background processes are in support of presentation.
How is payment in support of presentaton?
I can see that details of the author/producer for any presented object and even their preferred payment service may be appropriately described in HTML5.
However, payment is about exchange. What do you have in mind that is to be exchanged and by whom?
Then perhaps we can consider how HTML5 can be used to help express and execute such an exchange (or enable the browser to).
I had assumed you had in mind some way that HTML5 could be used to attach micro-paywalls to presented objects or something like that, e.g. “This content or full functionality can be downloaded/unlocked for $5”.