GTX 1080s can only do dual SLI right now first off, second you wouldn't ever really want more than two GPU's. There are several problems that can arise from using SLI, and while theoretically it should boost your graphics, using more than 2 will actually start to lower your FPS on a lot of games. Also, there is really no situation in which you would ever need more than 2 1080s, considering a single one is more powerful than 2 980s in SLI according to nividia.