I think you're getting away from the reason MSQ roulette exists in the first place, which is fine and not your fault - it's easy to forget since the content is super old:

New players need to get through the MSQ and the dev's don't want them waiting around in really long queues for Castrum, Prae, or Ultima Weapon. If they made the MSQ dungeons and trial part of the other roulettes, it would reduce the pool of bodies who are readily available at all times to help them get that quick queue. It would also mean that if you queue for a normal roulette, there's a chance you get a 40 minute long dungeon with unskippable cutscenes, which would result in numerous instances of players abandoning the duty since the timer would be shorter than the duty itself. So how do you solve this? You make it optional with its own roulette. In order to incentivize the broader player base to assist these periodic sprouts through these dungeons (and trial), massive xp and tome bonuses are awarded to the players who do queue for msq roulette. If you add different duties to the MSQ roulette mix then you get the same problem I posited above: People would just leave the duty if they didn't get one of the dungeons without unskippable cutscenes.

Crystal tower is already the most common alliance roulette raid by a mile and a half, so there's no shortage of players queueing for that. Additionally it would completely take over MSQ roulette since it would be removed from normal alliance raid roulette for the most part (which would change the level requirements for alliance roulette and then there would be a shortage of players since you're going from 4 to 24 player duties.....you see how there's all these logistics problems?). MSQ roulette is simply the dev's way of incentivizing us to play content we'd otherwise never touch again to assist new players.

You used to be able to skip the cutscenes, and guess how the new player experience was as a result? Player outcry was quite high. If you want to see how it would go, go pf a coils raid and run turn 1. Keep your cutscenes on and don't skip. lemme know what you find when you get out of the first cutscene.

Turning all of Castrum and Prae and Ultima Weapon into single player instances is a huge undertaking. Absolutely massive, expensive, and most of the players who will ever play the game during its lifecycle (even if it goes for another 10 years) have already played through the content. So why change it because a couple people don't like an optional roulette that most people never do anyway? It wouldn't make any sense spending those kinds of resources.

In short: Don't expect anything to change ever because most player either don't want it to or don't care, and the system is working as intended.