I've been using the new launcher, Google search, and hangouts from the Nexus 5 system dump since day 1 and it is working really well. You DO NOT need root.

As long as you are on your home screen, the "OK Google" feature works instantly. Hangouts has no issues with SMS, but I think the video chat is a little buggy (can't say for sure). The new Google now slide feature is also cool, don't know how much I'll use it though.

Just a heads up.