There has been a fair bit of discussion amongst developers on this point off thread, in emails mainly.
It looks like one of those dev's has gone ahead and put together a plugin marketplace, and I am sure he will talk about that himself in good time.
Personally I came to the conclusion that Moodle HQ has too many obstacles to overcome to do anything like a plugins marketplace. And for me it was enough to know that.
I am setting PoodLL up as an annual subscription membership thingy. Most of my other plugins will just stay on Moodle.org, but some will go onto the premium marketplace mentioned above.
I really like the innovations suggested in this thread though. And I hope some of them do happen.