umbraco/Umbraco-CMS — pull request #508 by lars-erik (2014-10-08 18:55:08+00:00)
Title: Don't ensure App_Code

We'd really like to precompile webs, you can't when App_Code is created every recycle.

I guess there's some obscure usecase where the system need the folder in place, so I assume this won't get pulled right away, BUT:
Nothing changed when I set up a new site without that folder or the EnsureFolder("App_Code") in place.
Nor did stuff like xslt templates break.
IMHO, people who use App_Code and/or use functionality within Umbraco that requires it to be there can just go ahead and create it manually.