Around 2.5 years later, and the landscape for Diesel 9 enjoyers remains bleak.
The old Coolsky website is completely shut down, as are the old FlightOne forums where you could ask about it.
The Sky Simulations DC-9 hasn't been updated in 9 months and the updates it received previously have failed to elevate it even above a default aircraft in terms of systems depth and accurate functionality, not to mention the whacky and inaccurate flight model. It does not seem like this is a viable project for anyone who wants a 'study level' DC-9 in the MSFS era.
JustFlight's successes with aircraft like the F28 and BAE 146 continue to position them as the top choice to produce a top quality DC-9. I don't expect anything more from the JF staff beyond a boilerplate "thanks for the feedback, we're not in a position to comment on future projects" response, or none at all, but I'm still out here tilting at windmills hoping this aircraft is perhaps on their minds as a future project.
The DC-9 was the mainstay of so many fleets for such a long time. We have the fantastic Leonardo MD-82/83/88, but no DC-9, and that is such a huge gap in aviation history to be lacking.