Not only would this directly permit players to add positions that have the mechanical power of rulers, it would also begin the framework for other positions that have mechanical power. It's those other positions that i need the categories for, so I have some idea what players would like to see mechanics for. For Judge, this is easy, depending on how the realm's government is setup, they'd be able to create laws, or enforce them, possibly by issuing bounties or banishments or the like. Because right now, literally the only position that has fleshed out mechanics, is the ruler.
Some of these categories will have pages of mechanics dedicated to them, while others may be little more than mechanical fluff for years (historian, for instance), but the framework would exist. Down the line, when we add something cool for one of these positions, I can tell the game that anyone with a position of type "coolstuff" should have access to it.
What's likely to happen is that critical positions will get listed in the realm summary, right under the realm banner. Highly important and Critical Positions would be listed below that on the realm's info page. All realm positions would be displayed in a page linked from the realm overview page. It'd go more in detail about what the positions are, and have filters so you could tell it that you only want to see extremely important military positions, for instance. Theoretically (this sounds fun to code...).
When laws are fully implemented, we could end up with a system where certain types of position of a certain importance (or higher/lower) and/or even specific positions or lack-there-of or whatever can vote on certain changes or do certain things.