You can spear all of the Rogues into the northeastern shed. And you can also have multiple people thieving on the same world without any loss to exp or GP. So long as all players click the chest within ~5 tics of the first person, everyone can still loot it. So you can actually have a whole team ready to kill aggressors on the same world.
That reminded me, whilst doing this all I could think of was the rev protections clans their used to be, because this is great gp/exp per hour if you don't have to deal with pkers. I think your right though, if you can get a bunch of friends you would make loads of money here and get some easy pks too.
So in conclusion you will end up with arthritis getting 99 Thieving 😊 Wouldn't the shadow veil spell help with exp rates? To lure the rouges use a Dragon Spear into the east house.