They are based on the idea that the neighborhood will blossom basically overnight into a regional destination like Camden Yards. I'm skeptical because we already have a thriving entertainment district in Old Town, but Old Town is too far from Potomac Yard to benefit from pre-game/post-game activity (2-3 miles with no direct transit links). Crystal City is closer and will get some bump, but it's still at least a mile away. Pentagon City is already a premier shopping destination so Potomac Yard wouldn't supplant it. That leaves residential. Heaven knows that Alexandria has a housing shortage, but an arena's existence does nothing to fix that problem. The solution to a housing shortage is to build housing where people want to live. People don't necessarily want to live right by an arena, they just want good transportation connectivity to where they work and good amenities in general.

Part of my problem with this plan is that it is probably DOA, but it is a distraction that has an opportunity cost - the cost of scaring away a more appropriate user of that space, a corporate office or something like that.