The documentation for this method has been pulled from the ionic website (see here). @mharingon, WTF?
Here’s the solution - https://stackoverflow.com/questions/34947496/how-to-use-nav-popto-ionic-2
// Move back two places.
this.navCtrl.popTo(this.navCtrl.getByIndex(this.navCtrl.length()-3));
FIX THE SIGNATURE IF IT DOESN’T TAKE STRINGS!!! Really losing faith in basic ionic functionality at this point…