Add more issue priorities?

A chat with John Swinbank revealed that issue priorities for HSC/LSST are mostly set by management (him), and that the Priority field is secondary.

The PFS ICS world may never have that kind of all-knowing management. Chats with Fabrice and Tamura-san suggest that adding a few more Priorities could help us self-track. Me, I'd start with adding a "Normal" Priority and making it the default. That might even be enough.