I can't imagine how you would implement such a scheme. For example, forcing Apple to allow non-Safari browsers in the app store is a binary choice, not something you can implement on a gradient. On top of that, market share tends to move around, sometimes a lot, so you would be changing the rules of the game constantly.

40% definitely is low enough to escape scrutiny as a monopoly, in any case. More than half of everyone who buys a smartphone chooses something non-Apple.