This quest is still in the game but the follow-up, where an engineer actually learns the tranquil mechanical yeti has been removed. This has been confirmed by the GM as being removed. So, completing the Yeti quest chain will not get you this pattern any longer per Scagarrde, Customer Service Representative
"Hey there!
I sincerely apologize that I was unable to speak with you directly, and for the wait you have had. >.< I hope that you are having a super cool day though!
It appears that the quest has been removed from the game.
Here’s what we need to do to focus on if you would like to see this changed and let the developers hear your ideas. We happen to have couple of venues that you can use to get this done. I’m not sure if you are aware, but have you heard of our Suggestion Feature? I personally like this option the best as it’s very convenient as you can do it while you’re playing, it is automatically forwarded to our developers, and unlike our forums it is just between you and them. To submit this we need to open the help menu in game and select “Submit Suggestion”.
The next venue would be our forum, found on our website at <http://us.battle.net/wow/en/forum/>. Others will be able to see your posts and openly chat about them. Sometimes this may lead to a more constructive idea, as others would be able to brainstorm along with you about the changes you would like to see! Just choose the forum that relates to what you would like to see changed and post your thoughts and ideas there.
The decision making process and all the changes that happen to the game is done by our developers, sadly not game masters. If you want more information about this new system check this out <<http://us.battle.net/support/en/blog/4684045>>
I hope you have a great rest of the day!"