Correct me if I'm wrong, but WebOS was open sourced after it started failing, and it was only parts of webos that were first "open sourced". I think the contexts are different, from day one b2g has been open source, and has had a contingent of supporters.
Plus, WebOS never actually got as far as FirefoxOS did on physical devices -- FFOS is powering phones for people all across the world right now. From what I remember WebOS got mostly relegated ot tablets.
I understand and share some of your frustration with their seemingly indecisiveness and willingess to drop certain projects to chase other ones. But can you blame them? They're trying to stay profitable.
So I think they'd have a little bit of an advantage becuase they've essentially ported the web model to run on embedded devices, and I think that could make it easier for manufacturers to integrate. Instead of learning to make some special kind of android app (+ ide support of course), manufacturers only have to worry about making webpages, and using some `window.mozFridge.changeTemperature` API, rather than something heavier.
My statement was more about trust than some implicit advantage in IoT (though I think the case could be made that they do have some advantages).