These types of marketplaces do exist but it is very difficult to justify using them. Why pay a significant margin (15-30%) so that we can use a pre-existing billing mechanism inside AppExchange or Azure or AWS. It makes more sense to maintain your own billing system and buyer journey. If the margins go down to 5% then it becomes interesting to give up that control.
I don't think marketplace is the metaphor I'm looking for. A single purchasing portal that takes maybe 5% to keep the lights on is more like it. A PayPal or Stripe set up by a SaaS consortium just to remove friction from the industry might be a good approach.
