I wasn't part of the selection process regarding Ember, which is the framework powering the entirety of dashboard-next. My personal feelings towards it are pretty ambivalent; as a python guy, I find it tastes a lot like ruby/rails (lots of magic). That being said, Heroku is a growing org, and a lot of people were involved in building out the new Dashboard — the strong conventions of Ember do make it easier for large teams to work together without multiple styles creeping into your codebase.
There's still a lot we'd like to do with Heroku Metrics, but we had to draw the line somewhere and ship a v1 that fulfilled a value proposition. Enjoy it, do (please!) give us feedback, and we'll iterate our way to yet more visibility into your app's behavior.