Building on that idea, I can see the sales pitch for this being something like:
1. You get the basic tools with the Master Tier subscription. That's enough to make simple, fairly generic settings.
2. You can separately buy more advanced kits, perhaps through deluxe editions of digital adventure books that include VTT maps.
I can see it being something like Dwarven Forge, where you can buy basic starter kits for not that much, but can also spend money endlessly (trust me) on encounter kits, special terrain, etc. Though I am sure that this will cost much, much less than DF.