Here is something I posted a few days ago regarding the likelihood of a future DC-10 or L-1011 type aircraft:
Not going to happen.
Anyway, this topic has been addressed before, and in case you didn't see it, here's a summary of what we pretty much came to agree on:
The MD-11, while certainly a good plane, has seemed to have found its niche as a freighter as opposed to a passenger plane. The MD-11 was just a few years behind its time. During the design stage of the MD-11, MDD was having a lot of internal problems that not only led to the delay of the -11, but also a total lack of Total Quality Management. Plus, consider this: the large, tri-jet engine was a design whose time had come and passed. From an economic and maintenance standard, why buy a plane with three engines, when a two engined plane (the 763, or even the embryonic at the time A330 and 777) could do the job just as well with one-third less the number of power plants?
All of that, along with the advent of ETOPS essentially doomed the MD-11 program long before the first delivery was made.
As for the possibility of a stretched 717 or rebirth of the MD-80/90, at this point due to the fact that the 717 sales just continue to stagnate, I have some serious doubts. Unless a big name airline like American or Delta steps up and orders 100+ of them, I'd expect to see that design fade into history as well.