I am an air traffic controller and this topic is very important to me because I am seriously contemplating a move to STL. I am 99.9% sure this is where I am going next and feel pretty good about the amount of traffic that will be there for some time. Consider this-
In the huge transcontential (connecting) market United now has the same cramped hub (ORD)to deal with and American now has three, giving the business traveler who has experianced the O'hare situation even more options.
Just like has been said in a previous post, I also think the STL hub will continue as a reliever for both hubs. I flew DFW-ACT last week. A 23 minute flight (scheduled for 50 minutes), departing terminal A and using runway 18R for take off (not a long taxi). We didnt sit in a very long line but we still got to Waco about 5 minutes late. As big as DFW is, it hampers the aircraft utilization rate.
STL, even with its close, side by side runways can move some serious taffic on, even a marginal VFR day, using the LDA approach.
Comparing STL to the west coast is a little off (In my opioin) because of the low cost competetion from some very established carriers like SWA and Alaske, then of corse there is United. STL has the potential to pull from every region of the country. If the cost structure of USAir was right I think they could of made BWI and PHL work at the same time. The catchment areas for STL and ORD are much bigger (meaning the whole country) and with the right A/C, schedualing and an appropriate cost structure I dont see why this wont work.