My wife got a Mazda6 about the time the rumors started about the diesel, which I was going to push. But it got delayed. Now seeing this it might be time for a trade in!
I had a 2010 Mazda6 with a V6. Fun car to drive. Put 95K miles in 4.5 years so I put that whip through the paces haha. I REALLY like the new look of the Mazdas so I expect the people to respond well to a diesel option.
I worked at a launch/training event for the new Mazda6 last week; didn't hear anything about a diesel so IMO the earliest you'd see a official release will be the 2020 model year (fall 2019).
PS - I do not work for Mazda. I work once in a while for a marketing company that runs events for automotive manufacturers.