This same dynamic would apply to Macs as well, of course. In fact, this very thing came this close to killing Apple in the 90s. They licensed MacOS to clone makers, who immediately took the high-end high-margin market, and left Apple to develop MacOS and sell low-margin, entry-level machines. It took the return of Steve Jobs to turn the company around. They were weeks away from bankrupcy. He immediately killed the clone makers, begged/threatened Microsoft into giving them bridge funding, and started work on the candy-colored iMac.
As for Android, well, it's nominally open source, but an awful lot of the stuff you need to ship a competitive OS is actually closed and closely guarded by Google. It's a bit more open than Darwin, but not much. If you stick to ASOP, you've basically got Froyo.
So, yeah, Chromium and is for real, and again it's a bit more open than WebKit in that it also includes the app chrome, and not just the web engine. But coincidentally, Google benefits from an open, standards-based web; it doesn't threaten their revenue at all. Go figure.
This fact has not killed Google because Google controls the App Store that has all the proprietary social media apps most people want.
Apple could dictate their App store and cloud services are only licensed/supported for use on Apple branded devices just like Google does and still keep the overwhelming majority of their market.
Open source won't kill a monster as big as Apple, but this rabbit hole is kind of moot because Apple will always maximize profit, consumer freedoms be damned.
A forcing function would need to happen like some of the scattered mandates in Europe that only open source software be used in some education, government, and critical infrastructure environments to avoid lock-in.
If enough did this Apple would have to open source or else lose support contracts to those that do.
That's what I will be pushing for longer term.
They’re both different cases, but, IMO, still apply.
If Apple open-sourced their platform, Microsoft could choose to offer Windows Services for Macintosh, and hardware manufacturers could offer cheap hardware that runs Mac OS.
Microsoft could follow up by stopping offering Office for Mac OS or to by letting it (further) fall behind the Windows version. Adobe could follow suit.
The Android Open Source Project and ChromiumOS have hardly made Google go out of business.
Would any significant percentage of Apple fans see an "Apple open sources MacOS" announcement and suddenly throw their Apple gear in the garbage?
Of course not. They pay for the support reputation and the pretty well marketed aluminum they can't impress their friends without.