I don't think the rules should force teams to take domestic players. It's been tried and challenged before, and on principle nations should be able to run their team how they like.
But.
If I'm running one of these sides without a professional standard comp, I want to be building a pathway and improving the standard and popularity of the locals.
How big's a WC squad? Let's say 24 again.
Of those 24 I want to take my best 7 local players. 17 overseas professionals, a full team, and 7 locals - approximately 1 for each on-field position.
I play an Origin-style local rep series as a selection trial, with the carrot for the players and fans that the best performers are getting a trip to Australia to play in front of big crowds, to get mentored by and play against superstars of the game.
If the selected players are lucky they get a game off the bench and even luckier they get noticed by a 3rd or 4th division club that can get them over here for a season or 2. Worst case they go home and improve their local team with what they've learned.
News outlets take notice of the 7 nobodies who went overseas to play Rugby League in Australia.
Connections are made - retiring players or players not likely to make top grade might be enticed to go for a RL season or 2 in their heritage country to raise the quality and IQ of the game.
Maybe my team doesn't make the finals. Probably doesn't. But really is there much different between a bunch of NSW Cup players vs Australia than a bunch of NSW Cup players and a sprinkling of talented amateurs on the bench? Not really.