Evidence for significant change:
1. Macosrumors article
2. Member wishes
Evidence for minimal change:
1. History. For the past decade, Apple has made virtually no aesthetic changes to its software between beta and final. Apple has repeatedly ignored suggestions / criticisms of its interface during betas.
2. Apple devoted a section of their public web site to publicizing and promoting the aesthetic changes (
http://www.apple.com/ios/ios7/design/). As far as I know, Apple has never changed an interface after posting a software preview to its public web site.
What am I missing?
At least that item 1 from "evidence for minimal change" wouldn't necessarily apply. The fact that no significant aesthetic changes haven't been made historically, doesn't mean that will apply in a case where there's a huge redesign of an OS as popular as iOS. This is the first time that is happening, so there's no way to really say that history would apply the same way to it as it did to other releases before.
As for item 1 in "evidence for significant change", it's not really just a MacRumors article, it comes from other sources as well, and mainly The Next Web, which has known inside sources and a more "serious" tech reporting credibility (for lack of a better phrase). That doesn't guarantee anything of course, but it does bring more support for it than just any random rumor article.
But, again, having said all of that, it would be fair to say that we can't simply say that there will or won't be actual fairly noticeable changes between now and the final version. We mainly just have to wait and see.