I know stadiums don't have to be close to DC, but the thing I don't like about NoVa is it gets pretty far out there before some area makes sense.
The 49ers stadium is actually down in Santa Clara and people figure it out. But I'd hate to abandon FedEx only to move further from DC to an even less accessible pace for mass transit.
Land closer is valuable and no-one in Arlington/Fairfax/Alexandria is dumb enough to buy pro stadium economic arguments anymore. That means you either need cheap land or willing local governments. You have to go pretty far out to find either unless you want to stay in PG
