I've practiced Judo on and off since the fourth grade, Have several friends who train in Aikido, one a Hombu dojo trained 6th dan, and have had the priviledge of visiting a Kendo dojo in Japan and to train at The Kodokan in Tokyo. Though a kilt might be comfortable I would never show up at any traditional dojo expecting to train in a kilt. All practical reasoning for doing it aside, this would be insulting to the art. The wearing of a Gi is as important as anything else one practices in the dojo. I don't know how a kilt at a dojo where martial arts originating from other countries are practiced would be recieved. There are of course some less traditional dojos practicing Japanese arts too, but in a traditional dojo, practicing a Japanese art, I'd say don't do it.