How to do issue triage in web-platform-tests?

Hi all,

I was speaking to Bob today about the infra
<https://github.com/w3c/web-platform-tests/labels/infra> label in
web-platform-tests, which we've tentatively made part of the Ecosystem
Infra Rotation
<https://docs.google.com/document/d/10och6DoxEe6AhQX7MiQR8AhtjDheKIlf-GpF0impeJQ/edit?usp=sharing>
but
haven't figured out how to turn into concrete steps.

The purpose of bug triage is to make sure that new issues are looked at by
someone, given a priority and possibly an assignee. In crbug.com there are
lots of fields that can be used and advanced queries, but for GitHub I
don't know how to do it. Anyone looking to triage all new issues for any
other label (corresponding to a spec rather than infra) might have the same
problem.

Some ideas:

   - Adding milestones for each quarter (or other granularity) to express
   that something is needed soonish. Searching for no:milestone could find
   untriaged issues, but then requires all issue to be given a milestone...
   - Labels that express priority, maybe priority:low through
   priority:urgent? Again requires every issue to be given a priority to be
   considered triage.

I can't come up with a way that doesn't require adding a milestone or label
to remove issues from the triage queue.
https://help.github.com/articles/searching-issues-and-pull-requests/ has
lots of good stuff, but using the update date or number of comments does
not seem like great proxies for an issue being triaged.

Thoughts?