Yes, YouTube doesn't have a first-party official app for Windows Phone, but what it does have is a collection of other great alternatives. This Windows Phone "issue" may actually be a better situation in one regard: the unofficial YouTube clients are always innovating to compete with one another.
This competition has resulted in Tubecast providing a new Thumbnails seek preview feature; this is similar to the one found on the YouTube desktop website, and exclusive to Tubecast on Windows Phone as of now. If you are a fan of Metrotube and have not tested any other app, it may not be a bad idea.
Tubecast has features such as the ability to download YouTube videos (even in the background), pin videos or channels to your start page, and more. Further, it allows you to cast to a TV through Chromecast and Airplay. It has 4+ stars on 3682 reviews, which is always encouraging, and you can find the download link below.
I am sure YouTube on Android and iOS will get these features one day, but without any competition there is no hurry.
— poppyto (@poppyto) October 17, 2014