It's true C2 lacks a lot of freedom for modular elements and teamwork. Other than a small team where people make assets and provide them for a developer, it would be rather difficult to work as a team. But, on the flip side, it is much easier to make big progress as a single person or small team than in a lot of other tools.
As far as finding a game to champion, I think multiple games is a better approach. I have full faith in Arima with lp, but it still may be a ways off until we really get to see it. I intend no selfishness, but I also would submit my own game, Courier, as an example of bigger things that C2 can do--particularly on the rpg front. There are some neat platformers already, and they'll only get better, but RPGs are lacking (for lots of good reasons!).
At initial release, Courier won't be gigantic. It will be larger than any other rpg project I've seen in C2, and most non-rpgs, but that isn't the point. The point is to treat the web as a unique platform, so that means early + often, ever-evolving and expanding, and freely available. So where bridges are knocked out and landslides have blocked paths, those paths will open up over time (and over development) to creat an ever-expanding world. And being web-based means changes can be made to existing areas organically and automatically, too. NPCs might not always say the same things or even have the same quests, buildings can be built, businesses can open and close (or move), and none of this is difficult to do in C2. Users also don't have to worry about installing updates since it will be the latest version each time they play.
It works now, the game has quite a lot of bigger systems, an inventory system (though admittedly much simpler than something like fallout), pleasing visuals, high-quality music, and is currently already larger than most C2 games and set to ever-expand. I say all this not to boast, but to explain that things like this are very doable in C2 and it handles them quite well. The ONLY problem I've had with C2 is it sometimes throws errors (or crashes) after previewing repeatedly. But Courier certainly seems to fit many of the qualities of a showcase for C2, and it isn't alone. I just have the benefit of releasing progressively, so it can be played sooner than a game targeting the end credits before release. Though I doubt I would ever have end credits... Just keep adding content even after the main story...