It's such an intriguing idea, yet it can't work.
kamper23 mentioned the logistics issue. It doesn't take a rocket scientist to realize that sitting 10 hours on a plane doesn't help an athlete's performance much, and then there's a little thing called jet lag. Then, consider how expensive it would be (especially for the Europe-based teams) to costantly keep crossing the Atlantic? And then there's the environmental viewpoint as well.
Besides, would this concept really attract the general public? European fans would probably be wildly interested in North American stars for at least a couple of years, but tears would be shed in the Nashville Predators office while looking at the ticket sales of their game with Slavia Prague. The thing is, the European hockey community has an interest towards the NHL, but the North American hockey community has very little interest towards Europe, besides obviously for scouting purposes. Good luck trying to market a franchise that's old and has rich tradition in Europe but is not known at all across the pond.
I don't understand why this overseas expansion stuff is still around. I've read about it every now and then for the last ten years and there's been no progress on the matter. Okay, maybe somewhere in the distant future, when people can travel at the speed of light at a low cost and the whole world has been united into one nation, an overseas expansion could be possible, butfor the foreseeable future it doesn't seem even remotely possible.