I had a friend visit from out of town and she wanted to visit a local bike shop to look at shells. I noticed a large number of wind shells with mesh vent panels in the back. I've seen lots of runner's shells with similar construction. The Patagonia Nine Trails shells have a whole breathable back panel, IIRC. Then I found a Shower's Pass windproof fleece vest with a stretch mesh back panel and I like it a lot.
I'm thinking of items for wear while active on the trail, where I'm wearing a fat bit if insulation known as a backpack. It's kind of like using a quilt, where all that stuff between you and the pack isn't doing much other than making you too hot and sweaty.
Overall utility is the caveat, but as I said, I'm wearing that pack 90% of the time. I could always add my rain shell on breaks or in camp if it was too cold with the back exposed. My hunch is that it would feel good to have my back dry a bit before heading on.
So why isn't a ventilated back panel more popular for hiking clothing?
Other bike gear revelations:
The Showers Pass eVent rain jacket looks really good for hiking. They even sell an accessory hood. http://www.showerspass.com/catalog/men/mens-jackets/elite-21-jacket
They also had an Elite Pro rain jacket that is 240g/8.5oz
http://www.showerspass.com/catalog/men/mens-jackets/elite-pro-jacket
There were two really light rain shells for minimalist protection. They need more research for lengthy use in the rain, but they are windshirt kind of light and both use WPB stretch fabrics, underarm vents, etc.
The first one that caught my eye was the Castelli Sottile Due jacket:
http://mikesbikes.com/product/castelli-sottile-due-jacket-187990-1.htm
The other was the Bellwether Monsoon jacket:
http://www.bellwetherclothing.com/bellwether/mens/outerwear/jackets/monsoon-jacket.html

