A couple of things I would find valuable:
1. As Cabbage has recently said in another posting "When I was Secretary I did propose that the Society make and sell 3 feet 8 inch wheels to cover all locos. This would still be in BR spec(!)". I would support this suggestion. I will need nominally 3'9" wheels for my Peak.
2. A track gauge that will fit GRS track, as the present one from the Society will not easily accommodate the wider rails. I suspect that a lot of people are using GRS track outdoors because of its proven robustness and weather resistance.
Tim