I think we could improve matters by abandoning the table and instead documenting these roles more like we document GUCs, i.e., each one has a section below it where we can document it in as much detail as we want.
One of the main attributes for the GUCs is their category. If we want to improve organization we'd need to assign categories first. We already implicitly do so in the description section where we do group them together and explain why - but it is all informal. But getting rid of those groupings and descriptions and isolating each role so it can be linked to more easily seems like a net loss in usability.
I'm against getting rid of the table. If we do add authoritative subsection anchors we should just do like we do in System Catalogs and make the existing table name values hyperlinks to those newly added anchors. Breaking the one table up into multiple tables along category lines is something to consider.