Why would Sony be relieved by this development? Because if Oculus was going to be bought by anyone, Facebook isn't a bad option at all. Facebook doesn't compete directly with Sony - in fact, it's probably quite happy to work with Sony. Sony doesn't want to make money from social advertising, while Facebook's interest in making money from games is fairly marginal at best. Facebook's money backing Oculus makes the contest between Rift and Morpheus even more interesting, but doesn't change the playing field all that much. What Sony feared, no doubt, was that Oculus would be acquired by a much more aggressive partner - again, the pair mentioned above, Microsoft and Valve, would be top of the list.
It's tempting to go a little further with this line of argument and say that Oculus has just handed a competitive advantage to Sony by seriously annoying its most loyal fans and supporters. Many will point out the correspondance between these events and those that transpired between Sony and Microsoft last year, when Microsoft's poor messaging and manoeuvring handed an enormous competitive advantage to PS4 without Sony really having to lift a finger. Oculus becoming part of Facebook - a company deeply disliked by plenty of core gamers - could be portrayed in a similar light, as a "betrayal" of those supporters which will drive them into Sony's camp. After all, whatever failings Sony may have, Project Morpheus has been presented to the world as a project firmly based within the Sony Computer Entertainment division and thus entirely focused on games. Just as Microsoft's incessant blather about television and other media made the early adopter audience feel like Xbox One was out of touch with their desires, Oculus' purchase by Facebook opens it to lines of criticism about not really being about games.
Microsoft is working on something to do with VR, while Valve is thought to have all manner of experimentation going on, involving everything from wearable computing devices to VR.Nonetheless, either of these firms would see a major leap forward in their efforts from an acquisition of Oculus. A high-profile entry into VR could finally justify the Xbox One's albatross, Kinect, since the device stands to come into its own as a controller for VR experiences; finally, a use that core gamers can get behind. Valve, meanwhile, would have been the most straightforward marriage for Oculus, as the company which has become the de facto platform holder for PC gaming took charge of the most exciting PC gaming peripheral in years.
Either of those deals would have given Sony serious pause for thought, potentially even leading to a change in strategy or approach for Morpheus. Neither of those deals actually happened, though. We're still left wondering what Microsoft and Valve are up to in this field, but barring a truly shocking announcement (and neither firm is given to Apple-style "here's our new product, and it's out tomorrow" unveilings) it looks like Oculus and Sony remain frontrunners. Only one of those is a platform holder with enormous engineering, manufacturing and game development resources at its fingertips.
Led by Minecraft creator Notch, a small band of indies have announced their withdrawal from Oculus Rift development since the FB deal. Oculus will no doubt be working to make this withdrawal temporary. If Sony's developer relations team isn't also working furiously to bring some projects exclusively to Morpheus while this upheaval is ongoing, they're missing a trick - and I don't get the impression that Sony's impressive third-party relations team has missed very many tricks over the past year or two.