BTW, I feel like I've left out the biggest justification for this, which
for me is POLS. What prompted me to submit the PR was that I actually
started writing an example of using Queue#each---it just made sense for it
to exist, so much so I thought I remembered using it before---and then
realized it wasn't there. To me it felt very natural and intuitive to
expect Queue#each to exist. YMMV, obviously, but #each is such a widespread
convention in Ruby that it seems natural to look for it on a Queue class.

OK, I'll shut up now :-)