Although I'm marking this as a duplicate for now, in truth I think of this more as not feasible. That's not entirely accurate because it can but done, but it's completely incompatible with the current subscription model and would probably need an overhaul of the software and the hub, not just the website, to make it happen. The only way you can do this presently is by having multiple hub entries with their own subscriptions.

This is by no means a trivial change. Our subscription model currently has a very basic premise: You subscribe to a hub entry for a given amount of time. That's the whole of it. What you're suggesting instead is a system in which hub entries offer a suite of products which can be purchased like a good. CheckPassport(), which just gives a yes or no answer as to whether a user is currently a subscriber, is obviously inadequate to the task because the point would be to check for new goods (and refunds, etc.) since the last time the game was played.

From a business model perspective there are a few more hitches. For one, we don't necessarily want to encourage microtransactions ad infinitum, as this vastly increases the possible percentage of fraudulent purchases we might have to deal with. Also, the $1 price tag is too low. Our subscription model doesn't handle anything that low anymore, not because we can't but because we won't, for the aforementioned reasons.

All that said, I recognize the benefits of the model you propose and it's currently in use by a lot of game sites and console manufacturers for DLC and the like. But there are significant drawbacks to trying to implement that, and it is a radical departure from the current system.