It is probably a culture problem if engineers constantly forget about review requests. However, it happens.
Having the little icon to show stale revision is very helpful, I think it will be even better if Phabricator send a reminder about the stale revision.
Some of this stuff got built at Facebook, but I'm not sure that it was ever really effective (@aran, I think you did some nag stuff?). Generally, I think this sort of thing tends to be annoying more than useful.
We might implement some kind of "digest" email eventually, and I still plan to fix the bucketing revision rules, but I don't anticipate implementing nag emails anytime in the next couple of years.
You could probably do this yourself over Conduit if you really want to try it. I'd be more persuaded that nag emails might be OK if I saw some evidence of successful implementations.
Thanks for the insight, @epriestley, do you have other recommendations on making revisions going through faster?