Grayson would be cool but I just don't like this universe they have so if they developed that I would want it to be completely stand alone.
I believe Sinestro Corps War was being optioned by Dan Didio for a film but never worked out. A series of GL films starting at Recharge and going all the way through Blackest Night would be pretty cool. I'd even like to see some of the New 52 storylines as well. They can skip War of the Green Lanterns, I don't think many people cared for it anyway