> There's some slowdown, but it all but disappears in an optimized
> build.

Hmm, I just built with --with-wide-int, and I don't notice the slowdown, perhaps because I also build with -O0 and --enable-checking=yes,glyphs, so it's already a bit slow.

> In any case, the time to make the decision is NOW, because this will
> need time for us to be sure any serious bugs are fixed before Emacs
> 25.1 is released.

Then perhaps we should enable it in all 32-bit platforms and just wait for the fallout. We can always fall back to the current default if things don't look good.