I think this kind of jacket is a unicorn for a reason. I've been on the lookout for a similar piece - light wind and precip protection for the uphills that's very breathable. What I'm saying here is probably obvious but...
A jacket that's in the 400 g range with pit zips probably weighs something like 325-350 g or so without them. That's pretty light, in the OR Ferrosi category. Any soft shell this light gets there by using lighter woven fabrics without membranes that are inherently more breathable, so they don't need pit zips. It just complicates an otherwise light and packable jacket that's already pretty breathable. Lighter jackets like the Alpine Start have lighter fabrics (which are even more breathable) and fewer zippers (no hand warmer pockets on the Alpine Start).
Once you start using heavier weaves or membranes, they get heavier and less breathable, so more likely to have pit zips, which makes the jacket even heavier and bulkier. But now you're in an entirely different weight class.
Another piece to consider (Patagonia Wind Shield Hybrid Jacket):
http://www.patagonia.com/product/men...&start=1&sz=24
I own one of these and it's sweet. The arm pits and back are breathable fleece. Keeps your back from getting too soggy with a pack on. The rest of the jacket is wind resistant light soft shell material and will shed light snow (but not heavy precip). It's more designed for running and nordic skiing which is why it's ideal for uphills.
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