Wikipedia reports that Amazon has a listing for Mork & Mindy Season 4, but no release time yet. You can request to get an e-mail of notification when it is available. This seems like a good sign that it WILL be released, and fairly soon. What do you think?

Paramount released season 1 of Happy Days, Laverne & Shirley and Mork & Mindy together. They released season 2 of those three shows together. Then, they released season 3 of those shows together. However, they released season 4 of Laverne & Shirley first. Later releasing Happy Days season 4. So I assume Mork & Mindy season 4 will be next. Then, onto season five for L&S and HD. That's my theory.

I am sure that it will come out eventually, it should be before the next seasons of HD & L&S are announced, but I don't think you'll find the info on wikipedia first.

Amazon almost always puts entries up for possible upcoming titles in series, it has no bearing on any possible release date whatsoever.