HP killed the Pre and TouchPad webOS devices earlier this year and then left the future of webOS to be decided later. Today, they issued a press release (PreCentral.net has a copy) announcing they are going to open source webOS, likely because they didn't want to put any more money into a dead platform and could not find a buyer. I suppose the remaining webOS developers will come up with some interesting ideas to install on legacy hardware, but imagine this just prolongs the death walk for webOS.
As good as webOS is, it cannot compete with iOS, Android, and Windows Phone today and I don't know why developers would spend efforts on the platform. When consumers hear open source and look at the support behind the platform, it is likely they also will expect free apps and not be too keen to pay much for anything. There are still active Apple Newton communities and very active Linux ones, but is there really going to be a market for this in the mobile space? I wonder if HP should have just killed the platform, but then we would probably have had the few webOS developers still around screaming bloody murder.