The current behavior would be the more efficient one. But it is also less clean, conceptually, so (I'm come to conclude) it shouldn't belong in the ref builtin.

This doesn't matter, though. It is a *very simple extension* to add this feature outside core perl. Something along the lines of:

use Inline C => << "EO_REFREF";

int
refref(SV* thing) {
    return SvROK(SvRV(thing));
}
EO_REFREF
[download]

(This is not anywhere near tested, though :)