Would you perhaps have any info/reference about where I could learn more about this reverse engineered PowerPivot API? This sounds pretty exciting. :D

To expand on my question, I'd heard (from Rob 'PowerPivotPro' Collie, former product manager on the project IIRC) that the core had been written in 'unmanaged code' (probably C++?), so I believe reverse engineering it would be a significantly larger effort than just opening some of its DLLs in say DotPeek, at least from as far as I've been able to tell.