I'm okay with integrating Google Voice to Hangouts.Right. I could see a case for integrating with Google voice though. Don't you find that app atrocious? It's also quite laggy for an app in 2014.
I don't care about integrating my carrier's number to Hangouts because I don't use my carrier's number for anything in particular.
While the Google Voice app is a bit clunky, it still does what I need.
If I can find an alternative on the Play Store, I would try it but as of now there is still no alternative.