Jimmy Carbomb actually had a pajama kilt idea going a few years ago. He worked out some deal with a retailer and that was the last that was ever heard of it.

I've slept in my PK MarPat and sport kilt a few times and it's really not that bad. It's usually when I expect to be having to get up in the middle of the night to check on the kids (storms, nightmares, illness,...) and don't want to have to fumble around for something to put on. I can just roll out of bead and head down the hall. The kilt does crawl up, a lot and I find the kilt sticks to the sheets so I actually turn inside the kilt when rolling over. I'll get up and the kilt will be askew but no problem, no one else is seeing in the dark.

I wouldn't do it in a "traditional" tailored kilt or one with buckles but a velcro adjustable so you can loosen it a little is fine.

When you make the kilt, don't cut the tops of the pleats out. Just pleat it up and run some stitching through it and you can remove the stitches and restitch it over and over until you get the fit you want. I don't think I would even bother sewing the pleats in like UK. Just a few from the waist down a few inches and let the rest hang. Your going to bed, not a dinner party