Seems nvidia has been trying to see how many ways they can downgrade SLI support without dropping it totally.
10 series: 3 and 4-way for benchmark programs only
20 series: no 3 and 4 way at all
30 series: only highest level card, and no SLI profiles
40 series: 1.5 way SLI and only on Titan ti Super, special SLI edition? I wonder...
50 series: 1.1 way SLI, only for Jensen Hunang, and only in his kitchen, and only to play 3d pong.