While it is possible to jump between pages and projects using “Copy as link” and adding that to an object, it is not as elegant as being really integrated into the prototype system.
I believe it would be much easier to add a third “context box” to the right of the frame object which can be a linkout to another Page, Project, or even into figjam.
The result of this would streamlined and compartmentalized flows, interconnected design libraries, the capability to move in and out of sandboxed external team flows, and more. A second result would be a huge performance increase again as prototype flows and libraries could be reduced in size.