@Paul M.
+1000
JBG wants it so they can tell their prospective Central Place tenants it's "close to Georgetown shopping". And Georgetown and Rosslyn BIDs want it to get more patrons from the other side of the river. So you're right. Let them pay for it 100%.
Then make them donate to a WMATA tunnel fund for having the privilege of ruining our skyline with their antiquated gondola.