Good point. That suggests a significant nonzero possibility that unless MS decides it's strategically meaningful enough to them to maintain a foot in the door on the browser space (much like Google chose to do), they might abandon the project, which would severely crimp the money-faucet for maintenance of the core engine.

This could, hypothetically, lead to a collapse of that ecosystem into an also-ran, in which case all Apple has to do is invest more in supporting their browser on OSs they don't own and we could end up with full browser hegemony... "If it doesn't work on Safari, it doesn't work on the Internet."