Interesting you should bring this up. Obviously if NW/DL did this by themselves they would lose all their elites, if they did it in collusion with everyone else, they would be fine.
Speaking of collusion, last week I flew a couple segments of Intra European Business class on AF and AZ (CDG-FCO) in paid C. I was truly amazed at how pathetic both those carriers products were intra-europe. Yet, that is a market in which no one gets upfront for free. Thus, I do not believe eliminating free upgrades is a panacea.
In my opinion, the European carriers are not the great carriers and saviors that some people make them out to be. Heck, on my AF CDG-IAD segments last week I was the recipient of the most inattentive and lazy service I have ever had up front.