It'd be great if it was more than just the roulette and if it was an optional difficulty level for all level 50 dungeons, have it give twice the tomes they currently give and maybe some extra drops. Though since you know, the only instanced content with relevant gear in the game has to always be Coil, the only other decent thing that could drop would be mats or maybe minions. Maybe they could do something with aetherial gear too, doing runs to get at least i110 aetherial gear with the stats you want would be interesting.

Aside from the challenge just for fun, extra tomes alone would make doing those old dungeons more worthwhile, it's not like people would outright stop queuing for the regular versions either. Admittedly it would take some work and this game is all about cutting costs and corners.