I have been helping companies understand their sku complexity. Not necessarily with a view to reducing numbers but at least appreciating what each new sku means for them. Some companies have real difficulty in delisting any skus even those clearly not adding value. I have taken a fresh approach and called on those over-paid players in the English FA Premier League to get people thinking out of the box on complexity. http://bit.ly/lz4iQp
Just analyze past few years of sales data for all the SKUs.I think it would definitely provide you some meaningful insights about the sales trend.Also,if a SKU is not performing well in a particular market/geoghraphy,try to find out the competitive landscape of the same.It may happen that a competitor is able to sell identical/marginal different SKU in the same geoghraphy after combining some extra/different efforts.
Moreover,you need to take Top management's view before arriving at the final conclusion.