As a flight simmer, I'd be more than a little enthused to purchase specialty transportation and railway games if they were interactive (which I would not do otherwise) for the added immersion factor of flight simming. The sheer magnitude of this endeavor would certainly dwarf a single company yet could be easily accomplished by many developers from various specialty parts of the industry consolidated in a "one" world platform.
Yes, definitely it would come with that synergetic effect. I'm just a little bit worried how such a mall will be able to combine the commercial and freeware/open source content into one platform, from the legal viewpoint. For example, I know that freeware simulators mostly don't need to bother with brand recognition, whereas lawyers are likely to go after commercial ones unless the rights were obtained, that kind of thing.
What we'd like to achieve is that you'd be able to see an Airbus by, say, Aerosoft, even when you didn't buy the plugin yet. That would be like an unobtrusive in game advertisement - you see a plane at an airport, you want it - you buy it online in-game, a plugin for its systems simulation is downloaded on the background and you are able to fly it right there. Same with any other kind of vehicles or activities. Content such as airports is different, but it too can be shown as downloadable content in-place, with automatic trials or in prepaid packages where you are paying only for the content you are actually using, etc etc.