Now that UW and Capitol Hill have a station, it makes sense to at least study the feasibility of an east-west line that could provide an alternative to at-grade transit and connect to the Link.
Another advantage of a crosstown route north of Lake Union is it could continue east over the brand new 520 bridge, which was designed to support Light Rail and connect to the east side.
As a resident of Seattle, the current plan is vexxing. I love transit, and I don't mind voting for something that I'll never see (as long as there are good reasons for the long timeline) but I'd certainly prefer a different set of priorities for light rail.