No, not retail 360s, used ones. Mark my words, CL will be
jam freaking packed with 360s this holiday season.
In fact, I can guarantee we'll see 360 slims for $100 or less easily found on CL in every metro area, with bundles to boot.
Regardless of backwards compatibility or not, old gen consoles ALWAYS, I repeat ALWAYS get dumped in large enough numbers to drive the price to the floor in the used market.
Hell, 360s are already nearly impossible to sell used for any reasonable price. I recently got in a Jasper 360, and had a hard time getting $50 for it, even with a 120GB hard drive and two controllers.
Prices even for slims are already mediocre :
http://dallas.craigslist.org/ftw/ele/4000599771.html
$120, Slim with 3 games, Kinect, Wireless pad.
I don't know if this is the first time you've ever seen a new console come out, but I've been watching this happen since 1985. NES/SMS come out, suddenly Ataris and C64s are $5-$10 at garage sales. SNES/Genesis come out (not backwards compatible obviously unless you bought were one of the 5 people who bought the SMS converter for Genesis) and NES/SMS were immediately piling up used for cheap. PS1/Saturn/N64 came out, all the previous consoles got dumped for chump change, etc, etc, etc.
It repeats every_single_time. Sometimes you have to keep your eyes open for the deals, but they're out there even in less than ideal situations. I recently got a Wii (red Mario limited model) with about 40 games for $35. A single one of those games was Xenoblade, which I easily sold for $100 by itself.
People just have no idea, they get a new system or get bored with the old one, and just dump the old. If the console is still current-gen, then prices support it to some degree, if the console is last-gen, then forget it.