I've seen this idea mentioned in a few places now and I want to nip this idea right in the bud.
Here's the problem I have with the idea of a fringe for Luminato. We already have a very successful fringe festival for theatre, comedy and dance. There's also a successful festival for photography. Many festivals for film. The week after Luminato has a successful music festival (who I think had to move their dates because of Luminato), one of two. So the only form that would benefit would be visual art/video installation, although one could argue that Nuit Blanche takes care of them.
All these festivals existed before Luminato. The artistic community is already very wary of the festival because of the way it came in and got a great deal of funding. To do a fringe would put these other festivals at risk and I can't see how it can be a benefit to anyone.
I've participated in the Adelaide fringe and honestly, it's overwhelming. Edinburgh is even more so. The reason those fringes exist was because there was nothing else there at the time. This is not the case in Toronto. I think we need an international arts festival and I'm glad Luminato exists. But it covers enough ground that we really don't need a fringe as well. And I will fight tooth and nail to stop one from happening.