**** SPOILERS BELOW ****
...My earlier prediction was mostly confirmed! Grogar is back, but he's now the head of the supervillain team hinted at in an earlier Hollywood Reporter article. But Sombra rejected playing second-banana to Grogar, preferring to take over the Crystal Empire, himself -- for which he paid a pretty hefty price.
As for the S9 season opener: I thought I had the plot figured out and I was NOT surprised when the Princesses took back their retirement, but the twists and turns kept the story interesting throughout. Conclusion: S9E01-02 is a GREAT episode!
This is shaping up to be a fun final season for MLP!