Thanks for taking the time to evaluate the Intel Media SDK. As you pointed out, there are a number of differences between the Media SDK and x264 in terms of configurability.
The Intel Media SDK is designed to be an API that takes advantage of the hardware of the platform QuickSync, and thus does not have all the control/knobs as some software based implementations. We try to balance the needs of the developer community against the complexity of the driver. We are always tracking user requests and recommending additional configurability settings if they make sense - and are possible given the interfaces available to use from lower in the stack.
1) Hard to say. The presence of reserved variables should not be equated with us releasing future functionality. Like I said above, turning on those params imply driver and hardware support to be active and ready to be used in addition to our API.
2) The Media SDK uses the hardware to encode, decode, and perform pixel processing. Adding additional decoders wont make much of a difference if everythings redirected to the HW for processing.
3) Right, besides Target Usage theres not a lot of control knobs to dial up best performance. There is however a great deal of documentation on getting the best performance from the MediaSDK. Id recommend checking out the Media SDK Developers Guide, the posted whitepapers, and of course this forum for performance tips/tricks.
Hope this helps