I wonder if the concept of a simulated castratto voice is not as much a matter of curiosity as authenticity, not a question of the prowess of past singers.
Just as Broadway (and perhaps opera) singers of the pre-amplification era frequently used a different tonal quality for projection, one can speculate that castratti singers sounded different (from current day and likely from each other), and some of us would be interested in hearing what that different sound was.
One can wonder how modern-day techniques might synthesize a range of vocals sounds one has never actually heard, but the effort would certainly be interesting.