I can only think of the retail model for comparison.
I think that the GM and Client software should be freeware and come with a starter demo adventure. (Rope them in!)
More adventures could be sold separately as modules that are activated within the GM's software. (Bought on the GM's account. Not the players.)
The Dev kit could be sold independently of the GM ware for people to make their own complete modules. (Modules still altered on the fly by the GM during play.)
Adventures made by indies using the Dev kit could be sold or given away as the dev sees fit.
If there is a central storefront for the indie adventures, you could set up a license agreement a-la Unity to share profits.
Other sales could come from expansion resource packs for the Dev kits.
Personally, I've had this idea since 2000 but never acted on it. I'm so glad to see someone with the same idea making this a reality!