I too was impressed as hell as seeing that first time - but the stock market seemed to be rather displeased (loosing 4% price following the news). That puzzled me at first, but those reactions make sense (for short term traders).
While the SC-network is relativly technology-neutral (yes, atm Tesla Model S only, but if they license the technology (which they wanted to iirc) everyone could charge there) those battery swap stations are kinda fixed to that particular drivetrain setup (battery mid bottom of the car, fixed size etc). Even Tesla themselve might have problems to provide compability with future car generations.
On the other hand, one huuuge improvement would be the energy output of a BSS compared to a SCS: The BSS could provide 3.4 Megawatt in peak operation time (90s for 85kwh) while balancing the load to the grid quite nicely given they have enough battery packages on hand.
That number ist just huge (still working to get my head around - on the one hand, one or two measily windmills can get that, on the other hand equals that the power supply for my university (complete with hpc and particle accelerator) - twice.).
Well, thats a good thing, isnt it? One BSS can perform as well as ~30 SCS for which 500k USD ist just shockingly cheap (other sources (read: quick google search for a number) say 250k USD for a SCS). Which is why I dont believe that number - it wouldnt make sense to build anything else then. 500k USD would make sense for the screwing mechanics, storage cost and stuff like that, without charging infrastructure and batteries for operation.
I still think its cheaper than 30 SCS which leads me to my conclusion:
BSS are cool, because they scale much much better than SCS, handle "charging peaks" much better and could be quite cost-efficient under high load. With less then 20k cars on the road its still a bit early, though (but isnt "2 years earlier than necessary" Teslas slogan?). Tesla could easily plant more BSS than people need / would use, especially if they really plan to charge 80 (?) bucks for it.