Well, the most famous Warcraft 3 mod is DotA; it always had very different gameplay from the base game, and it was eventually made into a standalone game (Dota 2) as well as inspiring many copycat games (like League of Legends). Now the same is happening in turn to Dota 2 with the popular mod Dota Auto Chess, which is even more different in gameplay than DotA was from Warcraft; it was recently announced that both the mod's original creators and Valve have separate efforts to make it into a standalone game. Similarly, in a slightly different genre, quite a few famous FPS games started as mods: Counter-Strike, Team Fortress, DayZ – even PUBG, the game that set off the battle royale craze (it was based on a DayZ mod).
In other words, mods can effectively serve as "early development" versions of what eventually become new games, while being developed in bazaar style.
I don't think you nor the other person that responded to me give nearly enough credit to building on top of something compared to coming together to build something from scratch.
For example, open the original DotA in the scenario editor and look how simple it is. Some of the hardest things in game development are already done for them. The DotA creator could basically churn on their idea trivially at that level of abstraction.
Of course, coming up and implementing a fun game is the "other 90%" of game development, but the WC3 kit also heavily constrains you the same way RPG Maker 2000 does.
I just don't think this has much relation to the original claim that bazaar-style development would help this game along. Scenario editors are just worlds different. Consider how much work Miegakure's creator would have to do to arrive at the sort of custom game concept or Half-Life mod we're even talking about. WC3 and HL both already existed, for example.
Anyways, my guess is that Miegakure was a cute tech demo, but the developer has trouble lifting it into an actual game. For example, they also created http://4dtoys.com/, and it looks really interesting, but it's also hard to see how to advance from that concept to a more polished game. As opposed to, say, a tech demo based on portals.
Well... I wasn't actually intending to address the original claim you mentioned, only to refute the child comment, "I am not aware of any good game that has been developed bazaar-style."
But it's interesting: I feel like you're describing two halves of a coin.
Mods take existing tech and iterate on gameplay rules to make a fun game.
Miegakure, in your supposition, has tech but no game.
Certainly, Miegakure's creator could not have developed it as a mod to an existing game. But once they wrote their engine, perhaps they could have released it and let mod creators experiment with the game part.
...In practice, that probably wouldn't actually work, just because it's hard to attract a modding community to a game that isn't already popular. But if a community somehow came to exist, the kind of trial and error that modders do sounds like a great way to stumble on the right gameplay concept that makes 4D actually fun. If such a concept exists. :)
In other words, mods can effectively serve as "early development" versions of what eventually become new games, while being developed in bazaar style.