I've gone through many clipboards, the old cardboard ones, metal ones that I've dented or that have dented me, the new particle board ones that that have rough edges and of course the cheap plastic ones with smooth edged that I love until they shatter.
Now since you make cell phone covers, why not clipboards.
This would be Awesome.
1. Make them in Legal, Standard & Memo size.
2. Make sure that the clip/arm used to hold the paper is both low profile and secure(a lot of times on the cheap ones I have to bend them so the paper doesn't slip out), maybe texture it or use rubber over-molding.
3. If metal hardware is used maybe have it Melonite QPQ'ed.
4. Texture the edges on the top and bottom for grip, maybe with your TSP texture.
5. And Last but not lease, use the Sand polymer, for it's enhanced durability/strength and so we can custom dye are Magpul Tactical Clipboard.