McGrath, you are addressing the - quite distinct - topic of chord voicing. Good guitarists will vary it even within the same key, bad ones just strum off, which is unsatisfactory whatever the key. I am quite sure that Will is aware of the problem.

Still, using more than two keys is a relief for the ears, particular of those who just listen (- are there any? -), but also to many players. A possible solution is to offer two events, one in D/G, and another one with a larger variety of keys, announced in advance. -

Those melodeons seem to have been designed for affordability; nothing wrong with that, and still an issue for many. But wherever the main problem is lazyness, in may be overcome if the reward is appreciated.

Idiomatic fiddle music should of course never be transposed; just mix it with other music in different keys.