The proposed 717-300 is somewhere in length between a DC-9-50 and a MD80. I think (from memory) it was 4-5 meters shorter than the -80.
I personally can't see it happening. Would love to see it but they are beating a dead horse. I think the 717 is a perfect aircraft for many markets but just doesn't offer the same degree of FLEXIBILITY as the family aircraft like the 737 / 32X. Not to mention commonality benefits. Just my thoughts...