The idea is to have providers of scenery, on the web, in a format the sim can download. Cached locally, of course, and possibly converted into the sim's native format. And then you tell your sim, "I want my global textures from these guys, and the "pretty good global airports" from these guys, and the "really awesome Arizona airports" from these guys. Whenever those guys update their scenery, you get (either automatically, or when you tell your sim to check for new scenery) the changes downloaded and compiled into the local cache and you go flying. This would make it much easier to get updated add-on scenery.

The scenery providers could be pay or free, or both.

I imagine (or perhaps just hope) that there would be a place for "scenery compilers," people who are not creating scenery but who are hosting compilations of open scenery that they have vetted, and that you could, with little fear of disastrous results, add to your sim's list of "places to get scenery from." These people would be performing the same role as the editor of a story anthology, only for scenery. Some editors would get reputations above others. Think of Ted's airports, but not as a place you got to download airports. Instead, it's a place you tell your sim to go to download airports.

Find a way to get another sim maker to buy into the open format, and it's possible that sim makers could eventually get out of the creating-scenery business altogether.

I don't discount the sweat it would take. Creating an open format that more than one sim can use (or derive their internal format from) seems like big work (and polly ticks). And if I've learned anything from reading your blog, it's that every design decision you make has a hundred and one consequences you never could have imagined. But at least as a waving-my-hands-around kind of idea, it sounds cool, doesn't it?