The problem is that there’s no end to improvements, especially performance ones. We shouldn’t rush 1.0 without being relatively satisfied with that release, since as you say many people are going to judge the language on that occasion. But we can’t indefinitely push back that event either, because many users have also been waiting for the stabilization of the language. Remember that version 0.1 has been released in 2012.
There will be alpha and beta 0.7 releases, with some time before 1.0 so that packages can be ported, which will ensure that new users testing Julia for the first time when 1.0 is out will have a relatively smooth experience. But the porting period can’t last for six months like a standard release.