Quibbling about whether this qualifies as "open" or not is arguing semantics, but I think recent history has shown that the Android model doesn't lead to the openness that its proponents had suggested it would.
There doesn't have to be an exact parallel between this and ActiveX for this to be bad. Mozilla announced about a month ago that they would be developing a not-yet-cross-platform set of APIs called WebAPI. Except they invited any one to participate. I'm subscribed to their mailing list and actively participating. I can submit patches if I so choose. Dash sounds like an almost-finished product that the rest of the community has to either adopt or opt-out of.
I'd also argue that languages on the Web should be held to a different standard than general-purpose languages, since there are five primary players and the Web as a whole will be worse off if some of the browsers refuse to implement what other browsers are pushing.