Now, I am just a disinterested observer here (with investments in Bitcoin and all major 2.0 cryptos) so I don't speak for anybody but myself here; but it seems to me that Counterparty has Bitcoin over a barrel somewhat, especially with respect to the unspent outputs, which would be quite difficult to selectively block on the Bitcoin end. It would quickly turn into a cat and mouse game. Bitcoin could implement code to detect and block XCP transactions, but XCP changes a few parameters and re-launches a week later to get around it, which causes Bitcoin to respond, which causes a new change in XCP, etc. ad nauseum. I don't think that anybody wants that.
If that go to this way then i think Bitcoin dev team shoot own leg in long run. New innovations choose sure other places like LTC if they make situation "development friendly" instead try kill all projects. And like XCP have make also good to Bitcoin when have burn btc:s and in theory make every bitcoin value higher and also pay miners fees so i dont see why here is not btc core team time talk about cooperation?