There is already a means to do this through an external contract where your business model may have a premium level to it through a subscription mechanism where you are added to a private group for a set period of time. Once your subscription is up, you are removed from the group. This is just another way where Facebook is trying to leverage their position, but it is their platform, so the capitalistic side of me says 'go for it' while at the same time saying to those wanting to take advantage of this feature 'set up a private group and charge what you believe it is worth'.

I know of ptiavate groups where the cost is $3,000 US per year to be a partof the network, and that's one of the cheaper ones.