Maybe this is just me, but I don't think the mist repelling would look very good while the fast projectile is moving ahead. It should work as normal wisp torch at the end of the path, but you'd probably have shot it at a distance and the mist would already collapse between you and the end of path, blocking vision. In other words, you wouldn't actually see much at all, and the mists flowing back and forth around the fast-moving projectile could look glitchy. They already don't look that amazing when moving fast with the regular wisplight.

A staff which functioned like magelight (and maybe spirit damage on top of that, IDK) from Skyrim could do better, since the projectile wouldn't have to move at arrow-speeds. It'd also require less inventory space, and eitr instead.