I think Msoft should have some kind of exchange program, but I highly doubt it. And this would piss off a lot of folks, me included. Yes, Msoft never promised HDMI and there is no guarantee that if they release a new version you should get it, but I think Msoft would alienate a lot of 360 owners if they didn't offer some kind of exchange program. And monetarily, I bet they could. Say you send in your current system and if it works, the system plus $100 gets you the new one. Msoft can then test your old unit, repackage it, and sell it with a full warranty. Do they have to mark it as refurb? If not, they could sell a ton of the old units for a slightly cheaper price.
But I would still bite on this. I'd probably do what I always do when I get a new system, give my old one to my brother or to charity.