Ayeeeeee, those are some good ideas there my friend o.o yes to both of those first points, Odessen would be perfect for them to set up a 'secret' base and all the yes to being captured by Val later on the way to Zakuul.

As for Revan and Meetra, eeek. So many good options there, PERHAPS (since it would be a shame to not include them both somehow?) Revan is alive and present on Odessen, but Meetra has been captured and tortured by Val, and Revan has been trying to free her... But since they're both old by now it's more difficult for him to match up to Val and Arcan so he has to enlist the Qyaari's help?

And perhaps said attempted rescue mission could result in their capture? And they have to escape down onto Zakuul to find Val and Meetra in the room with the Eternal throne?

And then... I envision a big confrontation of some sort (a la KOTFE minus the getting frozen in carbonite part? XD) where either Revan or Meetra (OR as you say, perhaps both? They're old and tired as hell by now I imagine and I know my Revan would rather go be with Bastila in the end XD) attempt to face Val and fall, but the Qyaari escape back to Revan's Academy on Odessen to reconvene with what's left of the True Sith they had trained? (:
With possibility to have one or two (one each, twins perhaps?) actual Sith Purebloods to be among them, descendents of Renso's sisters perhaps, who have been hiding out with Revan due to knowing of Val's influence over the Empire and blah blah?

.... Okay, brainfart over for now I think lol hopefully at least some of that made sense XD 

I KNOW ISN'T IT. I'M SO EXCITED. and I'm not ashamed to admit I legitimately cried when they showed the crystal caves because HOT DAMN THEY'RE SO BEAUTIFUL ;w; they're everything the crystal caves SHOULD have been o: