I think this is an absolutely wonderful idea! 💡
I feel on a RSPS for a minigame to be active there has to be a good enough reward to entice the people with end game gear otherwise there is no reason to grind it. Possibly make a few exclusive armour sets with a weapon that can be cycled for the raffle as a prize. Each time it's hosted a piece of one of the sets gets released so that way it will take time to grind out in top of the luck of winning the raffle.
Castle wars is one of my favorite minigames of all time so I fully support this!