I'm guessing that last meeting right before RotS Ahsoka mentioned was on Mandalore, based on what Rex said.
Interesting that the same episode lifts something straight from the old Clone Wars micro-series (
the knighting ceremony) while also directly contradicts it (Ahsoka most definitely wasn't there right before the Battle of Coruscant.) Not that I have a problem with it mind.
I had heard the theory that the Grand Inquisitor had once been one of the Temple Guardians, based on the fact that Filloni had said he had appeared in TCW and since there were no male Pau'ans ever showed up, that left characters with covered faces. That combined with the preference for double bladed weapons led some to make the deduction.
Personally, I didn't buy it. That is until I saw the clip they released a few days ago and noticed when he drew his sabre, the stance was *exactly* like the Inquisitor's and that the uniform was also very reminiscent.
I hope they get into the story behind this. Did he turn before Order 66 and betray the other guards, allowing Vader and the 501st into the temple? Or did he survive the massacre only to be turned by Vader later. Either way it certainly makes the character much more interesting in retrospect and puts his taunting Kanan about his lightsaber form into a new light.
Also accounts for how he was able to recognise Depa Billaba's training at a glance. As a temple guard he may have even instructed Kanan as an initiate. One assumes they do more than hang around the temple, guarding things.
I agree Yoda's new model looked a bit odd (but then so did Kenobi's & Vaders at first.) That said the shot of Ahsoka looking back over her shoulder at him felt light something straight out of a Ralph McQuarrie painting and is probably now my favourite image of Yoda from either show.
For those determined to kill off Ezra & Kanan, this episode offered a possible "out" for why they weren't around in the OT. Their increasing power meant that the Inquisitors were more able to sense their presence, thus they would have endangered any Rebel base or fleet they stayed with (just as Luke feared he'd endangered the Endor mission by his mere presence.) It's possible that ultimately Kanan & Ezra either left the rebellion for it's own safety, or renounce the order as Ahsoka did. Dying is still on the cards of course.
Oh, and just to reiterate: Malachor? Called it!

Seriously though, I'm interested to see where they go with this. Based on the trailer footage my guess is that they may have sort of melded what happened at Malachor V with what happened at Ruusan in the old EU. The former where rogue Jedi destroyed a world to defeat the the Mandalorians and the latter where the Sith essentially annihilated themselves and all the Jedi around them in a suicidal last stand.
Merging the two idea could mean the Jedi annihilated the last of the Sith (well,
last but two) and the whole planet with them (including any Jedi still down there) in an act that has forever shamed them. Clearly Yoda sent them there to teach them the price of fighting to win at any cost.