I think you would. I certainly wouldn't be happy with Apple for doing it, but I would definitely say it's understandable. Like you're saying, they're a business, they make business decisions.
The point I'm trying to make there is any problems that arise from this fall squarely on the developers choosing to embrace this new language. I'm not writing this comment to convince Apple to act differently. The original post didn't make those arguments to Apple. This is all directed at developers, trying to change THEIR actions and feelings.
So as a developer right now, given that you have a plethora of open tools and an open ecosystem, why would you choose to use a language where a company has the opportunity to manipulate you in the future? Why write libraries and provide support and do this work for free for Apple? Writing libraries for the benefit of the community provides some security in that no one except the community stands to benefit from it. You can go to sleep happy knowing that you're helping out your fellow devs.
Writing for the benefit of a community that is paired with executive power means that it can all be swept from under you. Your library is still helping your fellow dev, but it helps the fellow dev with OSX 10.12 more. Now you've contributed to Apple's bottom line. Was that your intention?
I completely disagree with other commenters in this thread that we have some obligation to be thankful for companies for putting out things with strings attached. I'm not a spoiled brat for not liking everything. These companies would be absolutely nothing without their developers. It's time the community sticks together and realizes the power they have. It's not unthankful to demand more. It's dangerous to get swept up in the excitement of new languages and to assume good graces. Look no further than what Apple has done to Webkit, LLVM, CUPS and more. First class on OSX, give back only what's not newest. Swift will certainly be the same way.