How would you go about defending a review, subscription or not? I mean what action is taken? Edit the review? Edit the content?

The only way I can think is to use JACLPlus and the AEC subscription component (I think that's what it's called). You set the editing or new submit rights for a new group you create with JACLPlus and then you "promote" the user to this group upon successful subscription. However, whatever action you allow for this users is not limited to a one-time event. A person will be able to edit a review or entry as long as he belongs to the "promoted" group.

The other alternative is Joomla Equipments subscription component which allows you to restrict access to a specific url. This would work in the case of editing an entry, you could limit to a one time action.

I know these are not the best alternatives. Unfortunately jReviews is not yet there, in terms of having a better integration or built-in payment/subscription capabilities.

This is not functionality built into jReviews. jReviews allows you to define which groups can perform certain actions on a very detailed level and for a lot of actions. But you will need 3rd party components to get the users into those access groups (JACLPLus + some other subscription component).

A review must have a rating, so allowing an owner to response is not a review, it's a response and it's not something you can do with jReviews at the moment.