Hey, that's a good idea. I might end up doing that for my big vise if I need soft jaws.
I fixed up an old Fuller 4" bench vise a few years ago. It was ROUGH. I literally found it buried in mud behind my (52' Ford) truck behind a carport coming off a barn. Like, right were the gutter spills out. It had been sitting there for a couple decades. 1990s at the latest, more like it'd been there since the 70s.... Anyway, rough. Instead of making new metal jaws, I took a plastic cutting board - one of those white plastic ones, maybe 3/8" or a little thicker - and made the jaws out of that. I LOVE it. First example that comes to mind is working on a carburetor. You can clamp right on machined surfaces and not worry about scratching or denting them. Because of that vises proximity to my welders, I do tend to get the plastic jaws kinda... "melty". It's amazing how well they've held up. If I remember, I'll post a picture. When they get too boogered up I true them up with a flap wheel on the angle grinder.