Your assumption that the 475th will eventually go to the CT for "the action", is more than likely wrong. From what I've read, CT isn't going to be an action based arena. Just an opinion, but I'd have to say that if you put together a place where dying actually means something (your character actually "dies"), people are going to fly even more timidly then they already do. I'm sure there will be some real nail-biters when you run into someone who wants to risk it, but I'm also pretty sure that's not going to be common place.
As Dan said, however, I'm sure we'll be in there fairly often for the historical aspect and the scenario like feel, which many of us "mindless furballers" do enjoy. The CT seems like it'll be a Scenarios On Demand arena, and that'll be a pretty cool option to have.
And your idea that the MA will eventually fade into oblivion doesn't make any sense. Just look at the Axis vs. Allies arena. If you don't want to fight a P38 in your 51, just head on in there. Not as many do. I haven't been around lately, but two months or so ago there were about, what, 10-15 people in there on a good night? For various reasons the Main Arena will always be the main arena. (Barring of course the initial few weeks of CT where everyone's in there constantly trying it out).