We tried this with our company and was successful in integrating Angular into an existing Durandal application (with some issues). This was done using Angular routing and two elements (HostCompose and ng-view).
We had to use JQuery events that hide the Durandal view when a Angular Route was found and vise-versa.
It was not possible to include Angular directly into an existing durandal View as the Angular engine never composed and the {{data}} was shown.
When using routing the router.navigate broke the browser back/forward buttons.. Never got to the bottom of this.
We abandoned this project as it was obviously more effort than the reward. To top this off Angular 2 is not (based of reviews) compatible with Angular 1.3.
We where/are going to replace all Durandal modules one by one. However we would not be possible to port/update angular 2 in this way.