They have been for a long time now. Apps are commonly written in Java, Javascript, scripting in lua, python, etc. The only thing they don't allow is executable pages of memory, which the Go previously required due to it's runtime.

Apple has been accepting apps in all kinds of languages for years, including: Lua, C#, Racket, JS+native wrappers, Java, C, C++, Ruby, Python, etc.

Their current guidelines only prohibit dynamic code download (that is: installable plugins from outside the App Store):

3.3.2 An Application may not download or install executable code. Interpreted code may only be used in an Application if all scripts, code and interpreters are packaged in the Application and not downloaded. The only exception to the foregoing is scripts and code downloaded and run by Apple’s built-in WebKit framework.

Aren't they already approving apps written in C#? What's different about Go?

They've been doing that for ages already.

Please do at least a cursory bit of research before commenting about an area you're clearly not familiar with! It will save a lot of time, and prevent FUD like this from continuing to spread.