I had this idea some years ago as part of an extended game for higher-levels to play within the game. You could implement the simpler version by adding a ClanID field to the room structures (using OLC routines to force the rooms to be saved). Initially, set everything to 0 (or whatever "neutral" is) and then decide how you want clan "ownership" to be granted.
o player and/or mob of said clan walks into an unowned room, or walks into an owned room and stays there for N minutes, or walks into it N times (would also then need a counter), or N players of that clan walk into it (a counter and a list structure).
o clan "buys" deed to land from other clans, or from NPC governing body.
o clan "captures" land in clan-vs-clan warfare... see above for ways to get it initially
o gods "grant" land in a radius around clan headquarters based on ... population? wealth? coolness?
Then you'll have to decide what it means to have "ownership" of land:
o npc's might help clans members and hunt/harass no-clan people or enemy clans
o clans might get revenue based on land holdings
o clans might have to pay upkeep for land holdings
o clans might be required to have a minimum membership for N sectors, or a maximum of N sectors/member
Sounds like fun!