I'm with you on the 'Team GB' thing, I think it is important to keep the NT's separate. Training a player up and seeing them compete in the NT is one of the most satisfying parts of this game and a GB team would only dilute this.
But I would definitely like to play in a more competitive set up with several tiers of teams. It would add an extra element to the game, making it more competitive and it would also create a more beginner friendly environment. Any new team in Division 2.1 will be at a stark disadvantage compared to a team starting in Division 3, 4 or 5 elsewhere.
Most people want to be competitive from the start, patience is not a virtue held by most new members of this game unfortunately.
There would be some serious questions to answer on how they could structure and set up a GB league though. I suppose they could just create the league's ranking everyone by their World Ranking? Or possibly a teams average turnover to discount for the advantage Scottish teams have playing in a smaller set up?
Either way, it would be very hard to keep everybody happy in the short term but it would be beneficial in the long term.