Besides the people already saying the performance difference is much larger, the memory savings are quite important too, and I'd argue the complexity isn't that

Besides the people already saying the performance difference is much larger, the memory savings are quite important too, and I'd argue the complexity isn't that bad either. Sure, NaN-boxing isn't completely trivial, but it's largely a one-time cost for quite a small part of the definition of your vm. It even brings some nice things with it, like being able to use regular 64-bit routines to work with tagged data, and having a single nice 64-bit int to copy&paste around while using a debugger, whereas otherwise you'd have a whole struct.