The principle of ' live and let live' is a bizarre way to look at this. That's not the real world.
Let's take out the cultural connection/loyalty to a code, like you and I have with RL, like white South Africa has to RU, and let's look at the competition aspect.
RU and RL are competing codes, just as McDonald's and Burger King are competing fast food chains. It's ridiculous to think one will give the other a leg up.
When RL split from RU in 1895 - and justifiably so - it created two competing codes, a dog eat dog environment, both fighting for the same players, the same audience. That's the consequence of the split. Sport is business, you don't give a direct competitor a slice of your pie.
Drop the vague "rest of the world" nonsense and just focus on the countries where the two codes have any meaningful footprint.
RU = British isles (Eng, Ire, Sco, Wales), France (south west), Aus, NZ, South Africa, Argentina, minor Pacific islands.
RL = England, Australia, NZ (Auckland), Fra (Catalans), PNG, minor Pacific islands.
That's it. The rest of the world don't give two hoots about either code.
England, RL is predominantly popular in towns along the M62 motorway in the north of England. This is where all 11 English teams in SL are from. Go a few miles outside these towns the sport barely exists. Major northern English cities, working class cities, Liverpool, Manchester, Sheffield, there is little interest in either rugby code. RU is predominantly popular in the south of England, wealthy suburbs in the Home Counties, and the middle class in the West Country.
Ire and Scot only RU is played, both in colleges, with RU being the 4th choice sport in Ireland, and second choice in Scotland - a distant second to football.
Wales, RU is in the blood. Football would have a significant presence also. Like NZ, RL will always be a distant second to RU. While Wales RU team sell out 74k Millenium stadium for just about every game, in 2013 the Wales RL team played a RLWC game in Wales and got 5k in a small stadium in Wrexham, that's an indication of where the two codes rank there.
France, both codes support is based in the south west, though RU far outweighs RL.
Aus, you know the situation there.
NZ, RU is in the blood, RL has a decent presence but will always play second fiddle to RL.
South Africa, RU is in the blood of the white populous, football of the black.
Argentina, RU is a minority sport, played in colleges.
So what exactly do you want from each of those nine countries for RL?
