I have been leading a good sized Angular app for work for the past 8 months, and upgrading from v2 to v4 has been painless, even while having an AOT compilation build pipeline set up - the only modifications we had to do was switch OpaqueToken to InjectorToken, to , and Renderer usage to Renderer2, and these weren't required to be done yet. We only did those changes to get ahead of the curve from the deprecation mess…
Angular CLI stabilization is a much more important news, actually. One of mistakes of Angular team - Angular CLI had to be ready before Angular itself.