Wing cases can be made from just about any kind of feather to synthetic materials.
One natural material that is not always thought about as a wing case material is the BIOT.
Yes, the biot(s) can be used as a wing case.
For smaller flies 1 biot is generally enough. On larger flies you can tie in multiple biots to get the wing case effect.
Biots are less likely to split like feather fiber wing cases
You could even add flash over the biot to make a flashback style wing case
Use different color biots
Use a fluorescent colored biots as a hot spot
Be creative. Experiment.
Thanks for looking