Support in this case is perhaps a wrong term, but Nvidia (like AMD for their cards and Crossfire) needs to make a SLI profile for the drivers to get the SLI working. Same goes for many other driver level features for DX10 or 11. Making SLI support is a both way street and requires co-operation with the dev and Nvidia, although actually Nvidia makes most of the work by them selves and supports the devs practically for free. Why there is no P3D driver support for P3D yet? Most likely for two reasons, there either exists some scaling problems still with P3D and Nvidia waits LM to make some optimizations to renderer or then P3D is just pretty low on Nvidia's priority list. It can be bit of both, too.It's not that Nvidia does not support whatever flightsim, P3D just doesn't support multiple cards in SLI...