Please reply to this thread if you are using this feature. If you can also provide some details of how you are using it, that would be especially helpful.
I will assume that no one is using this feature today. Thus it will be considered a non-requirement for a community interface to external commerce systems. @sambapete pinging you specifically in case you have input.
We do not have a concept of a right to buy a course. We only use the “regular” flow of student buys course when course is on sale. That’s why I didn’t comment on your original post.
Unless I misunderstand what you mean by entitlement. It sounds more like a reservation system or a put something aside than can be bought later on if the student chooses to buy it.