Im no dev but based on what I have read RPGM is extremely limiting in what you can do, and you practically have to break the engine to do any interesting stuff which leads to its own batch of issues and is why they swapped to Unity as it allows them to more freely create features they want in the game. I've seen other devs have similar sentiments about RPGM.
Last update was its more than likely getting pushed back to December, the reason being is Unity released Unity 6 and they had to convert the game to Unity 6 which ate a couple weeks.