Very interesting article, thanks for posting the link to it here.
I sense that MidEx is going to look very long and hard at the capability of either airplane, especially with competition from the major carriers inevitably to creep into their own markets carved out of the MKE, MCI and OMA hubs. The range comparison really sticks out, with the A318 going over 3000 miles. Also memory of a recent article in one of the airline magazines interviewed MidEx's chairman and he commented that they had wished for a much better price on the 717 and lamented the fact the 717 is not a member of an aircraft family. Something that could be interpreted as a more "Advantage Airbus" situation given their aggressive pricing strategies and their well known family concept with the A32X airliners. This might very well be an irresistable tool they could have in their "back pocket" to engage in long distance, point-to-point /non-hub locations to meet that competition if a carrier sets it's sights on 'rubbing out' YX. If any of these mega-airline mergers go forward, you had best employ aircraft that can easily fit a strategic scheme, both both long and short term wise as well as be able to beat back or react to short-notice market changes that suddenly 'show up in your backyard' . That means -Survival-.
Not to drift too far from the subject, but another airline that offered a similar product in some regards was Legend Airlines. Legend too employed the DC-9-30 in it's fleet, albeit on a much smaller scale. But look how AA was able to move into Legend's market at DAL using reconfigured F-100s? AA also had a massive infrastructure network behind it to wage whatever "war" it could vs-a-vs Legend, above all else, with with impunity. They could pick and choose whatever they wanted to do in that battle. Legend had a great product but appeared completely undercapitalized, along with it's vulnerability to fuel prices, while major carriers like AA could afford to engage in "fuel hedging" giving them a much better competitive advantage in their costs. Had Legend been a more substantially sized carrier with an aircraft fleet/network of mini hubs developed, employing "fuel hedging", etc., it -could- have sustained a concentrated barrage like that AA is known to be quite capable of. Things might very well have worked differently for them.
The long term fleet planning at MidEx is going to be quite interesting to follow. I place bets on them going for the A318 with options in the A32X family. They have to be looking at their huge neighbors at NW in MSP and DTW and UAL at ORD, both carriers which operate quite large A32X fleets, the UAL A32X fleet will get substantially larger if US is allowed to be purchased.