Now if you are envisioning having the best of both GPU worlds working in harmony inside your gaming rig there are some things you (and Microsoft) might want to think about. The first is that the overhead of running two different brands of GPUs is going to be a lot of work. You will need to make sure that you do not have issues with two very different driver models and keep both of them up to date. Outside of this the expected return is going to be much less than a more traditional SLI or Crossfire setup simply because the two GPU types are so different in the way they process information. We saw this very clearly when Lucid tried their hand at this, either you saw a loss in performance or you ended up with graphical anomalies.
This point makes us think that the multi-GPU setup might be something very different than just for graphics performance in a game. It is very possible that Microsoft might enable the ability to use multiple GPUs for their compute features. An example of this would be to have AMD push graphics and nVidia run Compute functions through CUDA. This would work well for Adobe’s Photoshop and Premiere applications as they work best with nVidia GPU running in the system. In game physics and AI could benefit from this type of configuration as well.
We still really do not know if Microsoft will be putting multi-GPU support in DX12 or not as the “developer” that confirmed it has not been positively identified and Microsoft has refused to make any official comment on the matter. For what it is worth, it would be a good idea for this to be present, but I just doubt that it will really be a Crossfire or SLI replacement that Microsoft is working on.