Testing the new adaptive sampling in Cycles recently, I think the BF should really place Stefen Werner on the shortlist of who to hire once they have the funding.
Why? He has (almost) single-handedly made Cycles 5-10 times faster in many scenes by way of committing the Intel Denoiser and Adaptive Sampling. Cycles itself has never seen such a leap in speed at any point beyond the early days, and they have greatly reduced the difficulty in creating baby-smooth renders that do not require much post-pro at all. In addition, it would be a shame to otherwise lose him to a company like Autodesk (Arnold) or Chaos Group (Vray).
Other possibilities (according to my own opinion) would be Troy_S (for his prowess in color workflow) and Alexander Gavrilov (for his ability to deliver sizable performance and usabiltiy enhancements). Again, this thread is primarily meant to offer suggestions, and I definitely have no authority to tell them who to hire. However, who would you like to see on the core team if you could make that decision?