Version numbers do not refer the completion level. 0.x version can be quite ready, 95 %, but it is not officially published.
What is now missing from NEM ?
Is that an essential feature ?
There are always some features to be added, but when can be said that the software is "ready" ?

I dunno what these people coming out with this 'not ready' shit are smoking. Bitcoin was up for sale for years at 0.whatever.
I don't know why it isn't on more exchanges, but ground is being lost needlessly. I have no idea why some people think it's good thing not to be over with as many people as possible.
NEM is still in experimental phase. Do you really want thousands, even millions, of people flocking to a platform that is still experimental?
It doesn't sound like a good idea when we even haven't left beta stage, this tech will manage people's literal finances which affect their daily lives. Developers have to make sure it's extra secure and stable.
It will be ready when it will be ready and when that happens more exchanges/people/companies will pick up NEM.