Peter - If something is possible , why not try it ? I was simply suggesting that trying to play in difficult keys is good for developing an ear for a tune and getting better at finding the accidentals (half covering , usually) .
And Paul Burke - Even I would not be too happy at trying to play in G on a Bflat whistle . For G I would tend to use G ,D or C , though an A is not too much of a problem , nor an F .