Living in Scotland nothing seems more natural than wearing a kilt to a funeral. I would dress as plainly as possible, though, as it is not an occasion for dressing up. Kilt, white shirt, black tie, tweed jacket, plain hose and black or brown brogues (preferably not gillies). I can understand from some of the comments that kilt-wearing might be regarded as odd where you are but I am very strongly of the opinion that you are who you are not what you wear.