Just one other thought I've just had, Is how about being fairly restrictive on the recipe, But allow 1 other choice in Malt and Hops
that is
Pale Malt
Crystal Malt
Chocolate malt
Plus a 'Magic Ingredient' chosen by each individual brewer
Hops could be Choose up to two from
Goldings, Fuggles, Styrians, Challenger Yada Yada Yada
Plus a 'Magic Hop'
Yeast . . . anything you choose.
that is
Pale Malt
Crystal Malt
Chocolate malt
Plus a 'Magic Ingredient' chosen by each individual brewer
Hops could be Choose up to two from
Goldings, Fuggles, Styrians, Challenger Yada Yada Yada
Plus a 'Magic Hop'
Yeast . . . anything you choose.