Start with the good. Europe has extremely passionate fans and enough of them in enough cities to sustain a NHL division, certainly.
Yet what they also tend to have is a culture wherein fans don't pay a lot of money for tickets to see a game. That's a real problem.
The NHL is a gate-driven league that is largely marketed to white collar fans now. The blue collar crowd can't afford to go to very many hockey games anymore. There are a couple of exceptions in markets where the teams have been bad for a long time, but most NHL cities keep ticket prices very high.
The bottom line is that the money that teams make from tickets is extremely important to league revenues, far more important than advertising or television contracts. The prevailing economic model for hockey in North America and Europe may not be compatible, at least for the present.
Any city can draw for a major event, where there are only one or two games total (like Helsinki, with Laine and Barkov in town). What about growing a strong season ticket base, for both major draws/stars on the weekend, as well as Tuesday night against a team you don't care about very much?
This is before you deal with the travel issue, not just the strain on the teams and players, but the fans who watch games. To work, road trips are going to have to be long. You'll only go to Europe/North America once per season and you are going to be there for a while. As a fan, if your team is playing a third or a quarter of its games while you are asleep or working, your investment in the team is going to be seriously hindered. We are living in an on-demand world, but sports is the last bastion for live televised events.
What happens when a player gets traded across divisions? How many players are going to be on board with that? That's a major lifestyle change, one that isn't yours to make, like it is when you voluntarily change leagues.