Did anyone see the interview that the head of Muppet Studios and Kermit the Frog had back in 2015? They said that they are still working on music rights, and royalties. They also said to keep calling and asking about it, because they would love to release them.
I had A Facebook page called the Muppet Movement. The main goal of the movement was to unite Muppet fans and show Disney we want Seasons 4 and 5. I tried to get some of the other Muppet fan sites including the folks on this very forum to join in. Sadly, it was meet with a disappointing result. A lot of the major voices in the Muppet fandom feel that if Disney was going to release them they would have done so by now. I understand it has been years since the release of season 3, but I also still believe that if the fans showed up then anything is possible.
Anyways, that's about as an update as your gonna get right now.