NV automatically dropping rares is a problematic system. It's made rares far, far too common. This was a large mistake on Blizzard's part. I can remember when 800 dps 1h'ers were sought after. Now? 5k on the AH; easily acquired. The entire gear curve was destroyed at this point.
Even if you vendor 98% of the rares you find, you keep the best 2%. When you do find a Legendary, you're comparing that to the top 2% of a large sample size of rares, and suddenly you realize, the Legendary doesn't hold value, and nobody desires it. I find it hilarious that people complain "I can't sell anything on the AH", yet at the same time want further increased drops.
To the point: allowing skill swaps for NV will put a final nail in the derp coffin. It's easy to determine which skills to use against which elite pack. If Blizzard allows this, the next "community demand" will be "I want buttons F1-F5 to automatically save my builds". Might as well just allow players to use all skills at once with any rune.