Another thing is that far as third party editors goes we really need to know what is planned from Scirra, as it would really suck to get half way through implementing one, and then have them add one. Why pay for one when one is free, and in the editor?
Then if they were to make it where you could add support for the editor it would change things obviously.
Not sure if, or how that would affect what Scirra would add as features. I wouldn't think that that was direct competition since they don't charge for "official" plugs.
It might make it easier for them feature wise, but they wouldn't want to worry about a bunch of unsupported plugs either.
And thus we're back to the whole asset store plug argument.