According to Celtic Croft, they also make the Feilidh-beag with sewn in pleats. I would love some pics to see how this is done exactly, especially the waist band and the concealed buckles.
You'd have to take that up with Celtic Croft; a feilidh-beag (the untailored lower portion of the belted plaid (single width), worn from the early 18th century (some might say earlier) to the end of the 18th century) with sewn-in pleats and buckles, hidden or otherwise, stikes me as somewhat of an oxymoron.
The utilitarian beauty of such a garment is that it can serve as a blanket, shawl, bedroll, beach towel, what have you simply by shaking the pleats out; purposes which would be wholly defeated by stitching the pleats in.
If you want a kilt with a waistband, sewn-in pleats, and fastened with buckles, that sounds an awfully lot like a modern kilt to me.