Personally I can see aspects of each one that could be appealing, and I don't really see why it wouldn't be possible to do both. A European Open, which is open to competitors from around the world, and a European Championships, which is specifically for European players.

My main issue is with the arbitrary exception to allow Japanese entrants. It's fairly commonplace in many sports, from Football to Athletics, to hold European Championships where the incentive is to allow European players to compete against European players, and to perhaps allow some Europeans to shine in a major competition, when they are perhaps not good enough to do it on the world stage. However, none of these events would undermine that sort of thinking by then allowing select countries to compete as well. The principle is to restrict it to European players, and it seems daft to both restrict and unrestrict at the same time.

If it was for European players only, and was an addition to the calendar (rather than replacing an existing Open event) then personally I'd be in favour of it, especially in the future when (hopefully) mahjong develops more popularity and major tournaments become oversubscribed.