Frankly, I want the big boys on my side when it comes to opensource code. I want them to use the code I write. Usually I indirectly benefit from them using my code anyway, and they benefit, and everyone's happy. This is true even if they decide to make proprietary changes which don't get pushed upstream. I gain influence in my community and lucrative job offers. I get invited to talk at tech conferences, and my projects (present and future) attract more attention. I honestly don't see the downside here.
Apple might have a change of leadership and decide to swim against the current and make LLVM proprietary, but if that happens can't we just fork it? As far as I can see, MariaDB is doing just fine. And until that happens (which will probably be never), we can get some huge compiler ecosystem improvements on Apple's dime. All opensource.
Am I missing something, or is this fear of corporations totally unjustified?