If anything it would further increase the effectiveness of premades. At least if you are pugging with people from your server you kind of have an idea of who they are, how they play, whether they are competent enough to be trusted with the ball or if you should even bother healing them. At least some semblance of knowledge that can help put you on a closer level to the 4 people running strats over mumble and coordinating with one another.
But even if that isn't true, things would just stay the same. Why should a premade team be any less effective against pugs from another server than they are against pugs from their own server?
Not to mention the whole "Premades stomp me" complaint is a bit stupid. There is absolutely nothing stopping anyone from making a premade in this game other than their anti-social attitude.