I have news regarding this. I have admob (both Banner and Interstitial) and Browser ("open URL") fully working.
Here the setup I use for getting this:
Construct 2 Project exported with Cordova Plattform.
Admob Plugin: com.cranberrygame.phonegap.plugin.ad.admob
Google Play Services for Android is automatically added as Dependencies
No further plugins needed (no InAppBrowser or others are required)
Cordova CLI 4.1.2 (very important)
Crosswalk Runtime: Embedded 12 (I don't know if this is relevant yet)
Both banner and Intersticial work fine but most of the time, expect long delays before you can see the advertisement shown in the screen.
And alse ensure you are online (Internet access working fine).
hope this helps.