I’ve thought this is a good idea myself in the past but I haven’t seen anyone produce it. The closest is some cycling vests (gilet) where they have a more wind resistant front fabric. But they are tailored for cycling.
Argon 90 for the front, then a mesh fabric for the back? Or no fabric, like a big hole? If you are wearing a pack, could it just be a simple vest that kind of clips on to your shoulder straps, to your hipbelt, and somewhere on the side, eg a mitten hook to a bit of compression lacing? Vest wouldn’t need a zip really (except for maybe right at the collar), if you get to hot, you could quickly make side venting, bottom venting happen.