Currently, Meridianum and Praetorium are the only 2 Main Scenario Roulette instances. I was wondering, if this can be renamed to "Main Scenario Roulette: 2.0".
Then an additional roulette can be made where Naadam is added - and subsequently, any other (currently available or 5.0) drawn-out main scenario battles. In order to make it "roulette worthy", more enemies could be added so that it could be done as a light party or a full party.
The purpose of the MSQ roulette is to get people into (and thus newbies through) Castrum Meridianum and the Praetorium.
Additionally they've said before that they can't let us replay solo instanced content - I'm guessing it's something to do with how the game keeps track of where you're up to in the story, and replaying it might trigger a 'duty complete' flag that resets your MSQ progress to that point.
(Presumably they've found a way to have multiple MSQ states, with 'new game plus' coming, but that seems to be an isolated separate tracking of your progress, and we still might not be able to replay individual battles at will.)