Actually the FaderPort 8 supports both MCU and HUI. You can open the FaderPort 8 in a dedicated Sonar mode by holding down a "Sonar" button during power-up. I've been using it with both CbB and Studio One; although the integration with Studio One is tighter, it does what other MCUs do with Sonar. Whether compatibility will be further developed for integration with specific CbB functions is anyone's guess. However with CbB now free and with no official BandLab hardware controller, it seems to me there's an opportunity for PreSonus to "own" the Sonar controller space if they want to, and more importantly, if they have the resources. Hardware controllers remain a relatively small market.
The FaderPort 8 manual has an entire section devoted to using it with Sonar. There's also an undocumented function...don't recall what it is offhand, I'll have to look at my notes. I was going to write a Sound on Sound column about using the FaderPort 8/16 with Sonar, but the manual covered everything so it didn't seem necessary.
Officially, the FaderPort 8 MCU mode supports Logic, Cubase, Nuendo, Sonar, and Ableton Live; the HUI mode supports Pro Tools.