This is the 1 3DS game I want more than anything.I've noticed that except with the GBA version the western one game 1 year after the Japan one.So do you think NA and EU will get it?

At some point, yes. I think it'll be eShop exclusive, though.

The DS game seems to have sold a million in the west (500k each in US and EU). That would be a big incentive take it to the west.
http://www.vgchartz.com/gamedb/?name=rhythm+h&publisher=&platform=&genre=&minSales=0&results=200

There is no reason why it shouldn't arrive to the west. It will be announced during the next Direct.

Really, what is it with this game that prevents Nintendo to even have a simultaneous release for Japan & US/EU?
There are about 100 words in it. Should be easy enough to translate!

Probably, but maybe as a eShop only, like what others have suggested

After seeing its sales in Japan (seriously, 80%+ sell through for a title like this is fantastic), I think so. I think physical is likely, but digital is essentially confirmed.

If it doesn't I'm gonna eat a kitten. Right in front of Nintendo's headquarters.

The last two titles got released, so I don't see why not.