I think it's besides the point of this patch to ifdef it out. If John wants a version of Python with this enabled, he can well enough build one without our permission. So it would be useful only if it was always available, and perhaps properly integrated into pdb.

IOW, I'm +1 for the patch. Having actual benchmarks would demonstrating the (expected) outcome (i.e. no measurable effect) would still be required to advance this.