A little late to the reply here but I'm a volunteer for openlibrary.org and I think they'd benefit from trying some of these things so I might share it with you.

What tool are you using to make the age reports? How do you determine if it's waiting on the submitter or the reviewer? Is it based on last comment? or requesting a review, etc?

There once was a tool similar to this that github bought and it was quite nice even for a small internal team but I'd really like to know what works well at your scale.

Cheers!