A black market is based on circumventing some prohibition. What prohibition is one circumventing to fight the Chrome monoculture? Google's success in creating a monoculture is based on making Chrome attractive and reducing friction with their services compared to alternatives. Independent of whether you think that's something they should do given their prominent position in some related markets, who or what is the black market going to be hiding from?

Not every person thinks the same or have the same moral believes. Only because you think that Chrome monoculture is a good thing with rational arguments, you can't assume that everyone agrees with that.

Just the fact that not everyone uses the Chrome engine today is a good indicator to that. Or that we are having this argument.

What will happen is that people not agreeing on Chrome monoculture will go else where. So even if you have the same engine, others have the possibility to create a total different web system. Now you have two different webs. To what gain?

Also an engine monoculture will eventually be treated as the de facto standard and the real standard will be ignored, i.e. implantation details will trump good design.

I'm not arguing in favor of a Chrome monoculture, since I don't want one. I just don't see how Chrome monoculture => black market happens. It wouldn't even had made sense as a response to the old IE monoculture.

Also the fact that this is even an issue is a product of HTML5, etc. leaving a lot of room for undefined behavior and being easy to misinterpret/misimplement. You don't even have to purposely bend the standard to try and create a monoculture; hard to predict implementation differences happen organically.

Black market is what happens who there is no choice.

For the old IE, Firefox happened (and other as well).

Okay, but what does Firefox's ascendance have to do with a black market? It wasn't even breaking some hard to enforce Microsoft EULA provision. IE got lazy, and Firefox offered a dramatically better experience. Whenever a new product overtakes a more established competitor because it's better, is there a black market involved?

My purpose isn't (just) pedantic. You claimed "No, forcing everyone to use the same engine does not give the incentive to refactor it into something nice. It gives the incentive to create a black market.", but then your example shows an incentive to make a superior product. It starts making a lot less sense in Blink's case if you change it to the more accurate "No, forcing everyone to use the same engine does not give the incentive to refactor it into something nice. It gives the incentive to create a superior product." Why not a superior product that starts with a Blink fork?

Okay, I get your point, however my focus is the word force. For me it means a gun pointing at your head, no choice.

IE did not force anyone doing anything, even if it had a de facto monopoly, therefore Firefox was created, because people chose to.

In this scenario I'm discussing it would not be allowed to create a Firefox, because everyone was forced to use Chrome, hence a black market is created.