> I assume, though, that Google will eventually make some change that Microsoft doesn't want, and they'll be forced to fork chromium.
This assumes that Microsoft still has a browser engine division by then. I suspect that adopting Chromium was largely a cost-cutting measure and this division is on the chopping block already.
I think they they had to kill their own rendering engine to keep Edge alive.
Sticking to their own engine would have eventually killed both. Hard to get people to adopt your browser if webdevs are not testing sites with it. And webdevs don’t care if your market share is marginal.
I believe the alternative would have been most of the enterprises deploying Chrome on Windows to access their apps. With this move Microsoft might still retain control of the app level. This is valuable because then they can for example provide integrated windows authentication for the apps.
I think it was a cost cutting measure too. But more about removing duplicated effort based on the premise that Microsoft was already spending a lot of time working on Chromium compatibility. And Google was inside Microsoft's decision loop. Microsoft was in the position of having to port every arbitrary evolution Google made to Microsoft products...browsers and tooling.
This assumes that Microsoft still has a browser engine division by then. I suspect that adopting Chromium was largely a cost-cutting measure and this division is on the chopping block already.