Having a light bonus to regular roulettes verses doing what's fastest til your brain melts would be a nice option, but I'm sort of with the rest of the responses here in that it seems redundant since so much content gives light.

Furthermore, it may be too late in the game to add it as Eureka's supposed to use an entirely different format to building our relics for Stormblood. We may never see a light farm stage for the new ones at all.

Personally, I'd rather just see the light stage get smacked with a good nerf and let the devs focus on making Eureka work.