Taiwan has embedded Line into their social norms in the same way as most countries have done with Facebook.
It's safe to assume that anyone you encounter, regardless of age or social status, is available on Line.
The branding is also very pervasive, doing promotions with convenience stores, clothing, toilet paper, and anything else you can think of.
It's won over Japan, Taiwan, Thailand and Indonesia.
It's gradually winning over Korea. (there were at least 5 merchandise stores in Seoul a few months ago)
However, growing out of those core markets hasn't worked so well.
Hong Kong has been targeted for a few years (opening a flagship store, and a few pop-up shops), and it gets reasonable use over here.
But it's not managing to kick WhatsApp or wechat. (I saw a recent stat of 35% of users)
So if they can't win over Hong Kong, I'm not sure how it'd work on Europe or North America where their "asian cute style" branding doesn't win them so many bonus points.