Apparently it was a performance issue with Roku 2 and why there isn't an official YouTube channel. Supposedly the new chip in version 3 should be able to get it, but if that's the case, why wasn't a YouTube app packaged with the new one?
A9 Chip Inside The Roku 3 May Finally Allow For An Official YouTube Channel - Dan Rayburn - StreamingMediaBlog.com
While the company isn’t giving any update, I think that based on the new A9 chip inside the Roku 3, an official YouTube channel could come to the Roku 3 shortly.