The DC-9 and MD-[89]X were great airplanes. One of the great tragedies of unchecked American corporate consolidation/acquisition is that Boeing was allowed to borg McDonnell-Douglas. (Although some climed the opposite was closer to the truth...)
Anyway, the resulting company is too large to fail, and thus, too large to exist. We're at a point where we could really use the competition we had in aerospace companies back in the 80s, when there were enough competitors in both military and commercial aviation for competitive pressures to keep the players working to provide innovation and value. (Rather than milking the market with intentionally poor designs a la Boeing's 737MAX.) Modern airlines have only two vendors to choose from now that Boeing and Airbus have gobbled up even their second-tier competitors.
Personally, I'd love to see what the old Convair, LTV, pre-Martin Lockheed, or pre-McDonnell Douglas might come up with in this competition...