"... as I know I can just do the traditional approach ( jacke, pants, and packcover )"
One way you could consider saving weight instead is to not bring rain pants. I brought very light rain chaps, and can't remember ever using them, and I started in late Feb. I just came back from a 3-day snowshoe trip were it was raining/snowing pretty much all the time and I still just carried my rain pants in my pack. Of course you might opt differently, but there are outfitters on the trail plus there's the option of something being mailed to you if you really want it.
Or get chaps, a light weight (~3 oz) option for if you really need them, with the benefit that you can put them on and take them off one-leg-at-a-time (which I like). Just don't plan to wear them in town while doing your laundry! :-)
Here's one place to look for chaps:
Or if you by a Dri Ducks rain suit, without too much work the pants can be home modified to become chaps.
If you do get a Packa, take care that the pack cover part is sized large enough to cover any pack configuration you might like. On my snowshoe trip this past weekend I had my pack loaded for winter, and it was a very tight fit getting the packa cover over that.
The nice thing about the Packa is how well it breathes/vents, and the ability to toss back the coat or pull it over you (or just the hood) is also nice. I guess what I'm saying here is that the weight is at least somewhat offset by the fact that for many people it's just a more effective piece of raingear.
Though that OR unit does look nice; I guess a person would want to combine that with a light hoodless rain jacket --- but who sells a good, light, *hoodless* rain jacket?!? Nice that when you want to take the pack off, you wouldn't have to pull arms out of sleeves to do it, and of course would still have a rain jacket on (hopefully with a hat of some kind). OTOH, it's overall kind of nice that the Packa covers the pack straps, waist belt, the whole shebang.
That's a big part of the advantage of the Packa, that by not being constrained by pack straps and waist belt, the Packa can vent better. It seems kind of telling to me that in the picture, the OR unit is being warn over a shirt, not any kind of other rain gear, nor does it look like OR sells any sort of hoodless rain jacket.