I think it's a great idea! It'd have to be a city with a major international airhub (Washington, DC? NYC? Toronto?) for the folks flying in (including from overseas).

A schedule like a class re-union weekend would work great: a casual "ice breaker" Friday evening at some local Celtic pub, and a dressier dinner-dance Saturday night with music. Saturday day could be for shopping, sight-seeing, kilt-making workshops, golf, whatever.

But, again like a class re-union, this would take a cadre of volunteers in and around the target city to organize the whole affair...!