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He says in his message it's been a slog for some time, looks like a good time to be done with it. Open source is great, we all like it, but demanding unpaid jobs can get old, too.
And it makes sense. You want Chrome in your tests if your users are using Chrome. Very few (if any) of your users will ever visit your app with a headless PhantomJS browser, so it's not a platform that you should go out of your way to support. I've been using Selenium Driver with Chrome in xvfb for my headless testing needs, and I've used PhantomJS for some automation things in the past where it was great, but since…
Things like reading the HTTP response code, detecting 404s on assets and catching JS errors in the console are all not possible with Selenium/ Webdriver, and I relied heavily on those capabilities in my Capybara tests.
While headless chrome might be able to replace PhantomJS for many use cases that doesn't necessarily mean the APIs will be comparable. In fact I'd more likely expect the Chrome folks to say "the webdriver API is it, because it's a standard." [1] Sadly IMO it's lacking compared to what PhantomJS was capable of.