[John McDaniel]

Can anyone parse this in terms of the AAX vs AAX DSP issue? What's between the lines here? Simply unwilling to take on the task or truly impossible?

We've just completed a careful investigation of AAX-DSP, and our unfortunate conclusion is that at this point, it's not possible to do a simple port of our native plug-ins to AAX-DSP.
Our plug-ins use advanced and complex processing techniques that don't translate well to the somewhat limited resources provided by the HDX cards (both CPU and memory-wise). Making AAX-DSP versions would only be feasible if we would recode the processing from scratch, and even then we're not sure we could match the features and audio quality in the native plug-ins while also allowing a decent number of instances per chip.
In other words, native systems are massively powerful nowadays and our plug-ins have been designed to take full advantage of these possibilities. This is great, but makes it harder to scale them down to a more limited architecture.
So for now, we will not start working on AAX-DSP versions of our plug-ins. Perhaps in the future if the HDX platform becomes more powerful, we might reconsider. We will of course continue to develop and improve our AAX-Native plug-ins including 64-bit support in the near future.
Cheers,
Frederik (FabFilter) - Apr 2, 2013