I asked Mike about this a while ago. Here's what he said about the challenges of it (this was a year ago, so I don't know if this represents his current thinki

I asked Mike about this a while ago. Here's what he said about the challenges of it (this was a year ago, so I don't know if this represents his current thinking or not): "Using 64 bit integers all-over will definitely hurt tight loops on 32 bit machines -- narrowing number ranges is very tricky for the compiler. Also, the fact that int64_t is neither a subset nor a superset of a double is worrying. This kills various optimizations and may give surprising results even in simple mixed-type expressions."