Cranky Flier has some good information from a Southwest source on KCI, which supports my amateur (but frequent KCI user) opinion. KCI limits what Southwest can reasonably do. It can't bank flights for connections and it shies away from pushing connecting flows through the airport because of congestion and crappy customer experience. The new terminal will change that, so when they look at a market like Kansas City-San Jose if the local market is a little marginal for a nonstop the better connection flow ability can make the difference. Or a market like MCI-BOS may be able to support 2x instead of 1x in winter. They don't promise the world, but I think incremental improvements will come steadily. http://crankyflier.com/2017/11/09/with- ... nsas-city/
Even if a new KCI was opened 10 years ago I don't know that Southwest doesn't still build the banked operation in St Louis. St Louis is a bigger local market and already (organically) had more nonstop links to the east before Southwest got serious about flight banks with Des Moines, Little Rock, Tulsa, etc. added. Plus St Louis being close to 250 miles farther east makes for less-circuitous connections between the east and places like New Orleans, Little Rock, Milwaukee, Minneapolis, San Antonio, Des Moines, etc. Kansas City isn't as perfect a mid-continent hub as people raised on the Mercator Projection map suggests because the earth is curved and because population density is mostly very sparse between Kansas City and the west coast. Even transcon traffic if you plot the great circle route connecting the biggest three west coast population centers (LA, SFBay, Seattle) an the biggest three east coast (Boston, NY, Washington/Baltimore) the routes converge roughly over the southern Great Lakes region, with a connection over places like Chicago or Detroit being the fewest miles overall. By no means is KC a bad geographic point for a hub, but I think some look a a flat map and thing it is the perfect place were it not for the terminal.
Anyway, I personally think this is great and that the KC region will benefit greatly even though odds of becoming a big "hub" are pretty tiny. But if 5-7 years from now Southwest has 20 more flights, KC's nonstop map has filled out nicely with more nonstop destinations, that's not a loss. And frankly when outsiders come to do business, go to school, consider a move, or even just connect through the Kansas City airport that first impression will be so, so much better than it is today. I don't think making a good impressions is a singular justification for any new terminal, but it will a definite benefit for greater KC.