This is interesting. I sat down at my machine on Thursday morning, and it was entirely unresponsive. It had warned me about installing updates the previous evening, but I've done this many times without an issue, and regardless, they are always complete by morning. I waited a minute or two for any sign of life (beyond the fans running), and then held power. I heard the unpleasant sound of the fans spinning up to high…
For added irony, my Hackintosh installed the update without missing a beat.
[1] Which is still terrible, these things should just not happen. Bad quality control from Apple' side and inexcusable for > 1000 Euro 'premium' computers.