You can now check your Yahoo and Outlook (previously Hotmail) emails inside your same Gmail 5.0 app. Google will launch this app soon. You do not need to install separate Yahoo or Outlook apps in your phones or other devices. Recently Google has updated some of their apps with Material design and expected the new Gmail app 5.0 will have the same.
Check this video for the quick look of this app.
Gmail 5.o app is expected to supports other Exchange Mail Servers accounts and 3rd party email accounts. Just waiting for the official release, may be it will be with Android Lollipop release.