Sandbox

There doesn't seem to be any way to add a comment to a task unless you are a member of the project? One extension in particular that I know of has a bug at a very low priority level (the project head hasn't assigned it to a dev yet) and there doesn't seem to be a way for a person (not the bug submitter) to expand additional information on the bug and/or suggest a higher priority level.

Yes unfortunately this is correct.

Only the original bug submitter and Project members can add comments to a bug report.
This is a known defiency and on our wishlist for addition to the forge.

Best i can suggest is making a new report, referencing the original report.