Gonzo and Rizzo makes sense. They are classic TMS characters and neither were performed by Henson or Oz. There has been a deliberate attempt to move Gonzo front and center since MCC. He was always the third banana behind Jim and Frank.
I think Frank Oz's limited involvement has hurt the Muppets even more than Henson's passing. When Jim was alive, Kermit was such the center that all of Jim's other characters were more bit players, even Rowlf. So without Jim, you feel the loss of the one character. But frank has Fozzie, Piggy AND Animal, three of the most important characters. I understand why Frank isn't as involved (He's made like FOUR Steve Martin movies and he doesn't even have to perform for Yoda anymore) but he was always the most natural comic performer and his loss is more keenly felt.