I've thought this idea over a little since first hearing about it, and I've come to the conclusion that it'd be insanity to admit one British team into the NRL.
If one British team were admitted into the NRL (especially if that team were successful), then it's likely that team would do what the Broncos did to the BRL teams (as BuffaloRules suggested) and suck all of the sponsorship money, publicity, interest, etc out of not only the ESL teams, but likely many of the current NRL teams as well!
A single British team would have a domino effect that would start in Britian with the smaller clubs going bankrupt as their sponsorship jumped into bed with the British NRL team in a bid to get their brand in front of the eyes of more people, then in a bid to get their brands seen by more eyes the sponsors of smaller teams in Australia would all leave their clubs and move to get in bed with the more popular clubs in Australia that have higher rates of viewers in both Australia and Britain.
So basically the majority of ESL and NRL teams would quickly become unsustainable, I reckon that give or take every club except the NZ warriors, Broncos, Rabbitohs, Bulldogs, Wigan Warriors, Warrington, St Helens, Catalans and maybe (basically I'm unsure of these clubs) St Gogre, Melbourne, the Roosters and the Eels would all go bankrupt in under 2 decades.
(BTW there were heaps of clubs in the ESL that I don't know enough about to say whether or not they'd survive such a change in the structure of the step up of the sport internationally, so I left them out of my list of most likely (and I stress most likely) survivors, but there's one thing that I can say for sure, that significantly more of these clubs that I left out would go the way of the dodo then would survive.)
This would kill the NRL's access to most of the markets that they have direct access to at the moment to in favor getting their foot in the door of one big one (Britain), and there'd be no promises that once they got their foot in the door that they'd be successful in the British market.
So the only way to alleviate that risk of creating one club so powerful that it crushers all the others and still gain access to the British market, would be to admit multiple teams from Britain into the NRL!
Admitting at least 6-10 would spread the sponsorship money, interest, etc out enough that you wouldn't create a team that was so large that it kills all the smaller ones in it's wake, but it isn't feasible to have teams crossing across the world so many times a year to play games against each other, so these 6-10 teams would have to be introduced in a conference.
Also some sort of system would have to be figured out that saw teams from the British conference and Australian conference play a certain amount of teams from the opposite conference in a year (for example each team would play each team in their conference once/twice/whatever and 4 teams (2 home and 2 away) from the other conference once, or something like that), otherwise I can't see there being enough added value or interest from the fans to make a British conference worth the the initial investment that it would cost to set up let alone the ongoing costs it would gobble up to keep it running.
Even still if you introduced this British conference you'd still be killing the ESL and maybe a few NRL clubs, there's no way completely around it that I know of, however you do it there'll be losses.
So now it comes down to the real question would a British team or more realistically conference be worth sacrificing the ESL, the majority of the ESL's clubs, possibly the RFL it's self (at least as we know it) and most likely at least a few NRL clubs!?
I reckon it would be worth it, but only if the NRL were 100% certain that it would work and the added money would not only cover the costs of running this British conference, but greatly increased the NRL's income and ability to spread the sport as a whole.
Unfortunately you can never be 100% about anything, and I think that the risk would be much to great. Worst case scenario if the plan failed it'd likely take the sport back to a similar position to what it was in in the 70's in Australia and in a much worse position in England.
Come back with the idea of a global tournament when Humanity has developed a much faster way to travel, or when RL is a lot more popular in Britain and NRL (or a similar company) makes hundreds of billions of dollars, then we'll talk about it again.
