Either way I turn this over and look at it, I come away with this announcement being the best possible outcome for WebOS. If HP couldn't sell it and they have plans to use it as they have stated then the shear size of the company should help keep things rolling while the community picks up steam. There are other companies that may also want to leverage this as a bargaining chip and may even decide to use it.
If HP can successfully migrate the code to OSS and provide for a strong governance I don't see why it wouldn't be a good contender in the market. If you think about it, Windows 8 is to be a web application OSS and so this is its counterpart in the OSS community. The two could and likely would see synergy from each other in the app arena. Another great thing about that is that if such a strong development community is formed based in web apps then we would see applications become much more portable I think.
Worst case I can come up with is WebOS falls flat on its face but even then I would expect some its best features and components to be picked up in other mobile platforms.
Granted that a mega corp buying it and throwing money at it would have been awesome. That not being the case I can't really imagine a better out come myself. Anyone else?