The Master Plan for DC Union Station has 8 tracks leading to the First Street Tunnel (same as it has now). Whether the platform mix will be 3 high levels and 1 low level or 2 high level and 2 low levels for VRE is likely something that gets hashed out during the design of the rebuilt lower level tracks and expanded mezzinine boarding. If it is 4 tracks with low level platforms, that is a lot of capacity for placing a Superliner train there for an extended boarding time, even with more daily VRE trains.
But this is effectively an academic discussion because the Long Bridge replacement is at least 10 to 15 years away from getting built and opening for service. Even with a new bridge and 4 tracks from Alexandria to L'Enfant Plaza, VRE is not about to become that busy with service frequencies.
