I could get behind a 24-man raid roulette.

As for a Roulette that handles the Coils and Alexander, I don't think that would be able to stand on its own. However, it might work out if those battles were shuffled into Mentor Roulette.

If an actual 8-man raid roulette were added, there would need to be some pretty significant changes made to the paradigm if they wanted people to bother with it at all. Since the odds of completing a lot of 8-man raids with a thrown-together duty-finder group (and, very likely, with some players new to the encounter), the odds of actually winning the thing would be depressingly low. There would need to be rewards offered for PARTICIPATING, not just for clearing, and those rewards should only be meted out after spending a sufficient amount of time practicing.

The rewards would need to be substantial, as well. An 8-man raid has a 90 minute timer, and many groups will run that timer out. During 90 minutes, a player could be doing a lot of other things, so they'd need to be sufficiently rewarded for the time spent. At a minimum, I'd say that tomestone rewards equivalent to Expert Roulette should be rewarded for every half hour of participation, so if you ran out of time you'd still be walking away with close to three hundred of each kind of tomestone. The rewards for successfully completing the fight should be similar, so that players aren't encouraged to just wait out the clock for the big rewards. For similar reasons, there would need to be evidence that the group is actually TRYING; any player that just sits at the entrance doing nothing should not be rewarded.

These are some pretty significant changes to the way Roulettes currently work, and SE has been pretty resistant to making even minor changes to their existing system (Glamour, for example, needs a big overhaul, but even just unlocking level and class restrictions would make a lot of people very happy - and that SHOULD be easy to do), so I'm not gonna hold my breath! Certainly it's the case that if 8-man Raid Roulette was added working as current Roulettes do, no one would touch it with a ten foot pole.