People bring up Portland because it is one of two commuter aerial tramways in the U.S. and because Portland is considered a model of livability.
But actually the primary function of the Portland aerial tramway -- free access to and from the OHSU campus for people who use, work or study there, bears virtually no similarities to a Rosslyn-Georgetown connection. Georgetown and Rosslyn are already linked up by existing transit, wide roads, sidewalks and shared bike paths, and the elevation difference does not necessitate a sky tram (to compare, the OHSU campus is 500' above the waterfront terminal station).
The only way I could see this gondola being workable like Portland is if it linked up a difficult to access portion of the northern or western Georgetown campus -- of course, GU would have to pay for most of it. If that can't happen, there's not really a reason to build it other than for tourism. GU put $25k into the $200k study, so I'd say its interest is lukewarm.