We know for sure that Doom Train is coming as Yoshi clearly hint it during the Anniversary event room. The only thing we don't know is when is coming. It may come in 3.2 and not now. He said he will reveal the next Primal during the event and it came to be Doom Train. I think we won't see a new primal now. I really wonder why no info yet except if Yoshi want's to surprise us and kept it a secret of the last moment.