717-100, maybe. 717-300, probably not. Seattle is VERY protective of their 737 product line and they do not like the thought of a Long Beach product cutting into that market.
There is increased interest in the -100, but Boeing is reluctant to launch the derivative without ~50 firm orders in hand. The only hope for the -300 would be if a major or semi-major carrier that already has (or consiering ordering) -200s and demands 100% commonality within the fleet. This is where Airbus steps-in immediately.
In the case of Midwest Express, they are going to use the 717s to replace their DC-9 fleet, but the -200 is not a replacement for their MD-80s. The -300 would be bigger and have longer range (which the -200 sux at), but not quite the capacity of an MD-80. It all depends on how large an aircraft they want to operate.
If Boeing goes ahead with the -100, they will use the first 717 test aircraft (T1). Yep they will chop it and put it back together again. A decision on the project (either way) is still probably many months away.