Here's my take since we're all weighing in and are all in different levels of shock: IBM needs Redhat to stay relevant. The way I think about it is in a few ways. 1) IBM's stock price has been tanking because I think they're not investing in new products but just cutting expenditures to meet stupid Wall-Street targets. But with the introduction of RedHat they get new "blood" as it were. Who knows, what if they make the CEO of RedHat the CEO of IBM a la Satya Nadella and Microsoft?
They have said that RedHat would remain an independent part of IBM as part of their cloud push. Let's take them at their word unless they prove us wrong. Also, if nothing else, this could give RedHat even more money to make ambitious bets -- perhaps we might see Power9 systems running Fedora soon?
In the end I think this is, on the whole, a good thing. Now, does MS buy Canonical?