I was thinking along the same lines, the oval shape would be the hard part, well that and no Habaki to hold the blade in place in the saya. But little things like that haven't slowed me down yet.
Lack of good saya making tools has, anyone willing to make or trade tools for sheath work letme know.
I could stack and glue leather together to form the basic saya shape with cutout for the talon hole and blade. Then wrap in upholstery hide, then the possibilities are endless for texture and color. A butt joint and cross stitch would finish a very expensive saya very nicely.
For something like that I foresee an easy 3 to 400.00 and a lot of construction time.
Might have to try in in miniature on a Ruki and see if the theory holds.