This would use the same dungeons as the High roulette, but when you entered the dungeon your iLv would sync to the minimum requirements for the dungeon. If the devs wanted, they could also revert older dungeons back to their original difficulty for the roulette (Bees, anyone?). As this roulette would be more difficult and time consuming, the reward should be more than current High Lv roulette, and it would be a nice touch to have the original loot drops in it as well.
The devs have said that they don't want older dungeons to become completely obsolete or way too easy (i.e. the current 110 iLv cap) so something like this could help bring life back to the older dungeons. There are some small issues though. For example current roulettes help to fill slots in groups that would otherwise wait a long time to fill and this suggested roulette would not as only people who signed up for it would be thrown into it.
It sounded like a fun idea to me so I thought I'd throw it out there.