Yea but this one has a timeframe attached. Mac Pro identifiers in an OS simply means there is an update due at some point in the future.Like the Mac Pro is coming?
http://appleinsider.com/articles/15...-to-new-mac-pro-found-in-os-x-el-capitan-code
There was once a prototype MBA on ebay with Tiger even though by the time the MBA came out it was only shipping with Leopard.