This was brought up a couple days ago during discussion of a game built in Rust on the app store. A comment there[0] claims that the restriction on languages is no longer in the guidelines.
In fact, it was only in the guidelines for a few months back in 2010. I can only quote the response to the comment you linked:
> This rule got so much press 7 years ago that it will be one of those "truths" about a platform that never dies on internet forums, that and the Playstation platforms using OpenGL as their primary API...
[0] https://news.ycombinator.com/item?id=14302931