With the 'two tier' idea, which seems to work, if a player like Tyson Frizzell plays for Wales, does he qualify for GB? Or can he play for Australia?
There are a lot more Australian born players that could qualify for GB, problem is they only seem to want to play for Wales/Scotland/Ireland in World Cups. Heres a list of high quality players that could qualify for GB through the celtic nations.

Lachlan Coote (Scotland) Matty Russell (Scotland) Kane Linnett (Scotland) Euan Aitken (Scotland)
Peter Wallace (Scotland) (to be fair he was injured) Danny Brough (Scotland) Ben Flower (Wales) Rory Kostjasyn (Ireland) Luke Douglas (Scotland) Tyson Frizzell (Wales)
Adam Walker (Scotland) Rhys Evans (Wales)

The older generation remember when Great Britain was the best at everything and we ruled the Commonwealth and half of the planet.
Sadly, those days are long gone and apart from the emotional value attached to the "Lions" brand, we shouldn't go back.
Having said that a "Lions series" against the Aussies would sell, no mistake AND the BBC like stuff like that so, it would get decent exposure.

More like good riddance. Your horrible emipre collapsed after WW2..

And the best at everything.. please! That older generation have a warped version of history.

I don't think this would sell as well as an ENG v AUS series marketed as "the ashes", particularly for the London fixtures.

Think beyond this week.

Like I mentioned, what if RL really takes off in Merthyr and they produce players good enough to play for Great Britain?

If GB existed now we could easily have Frizzell playing for us, so it wouldn't be exactly the same. Two Welshmen were good enough to play in the Grand Final last month, its quite conceivable the next two Welsh lads to come through (wherever that is) could be good enough for GB.

Frizzell would still be choosing the green & gold over GB.

Get real!