Yeah, I got a little excited about this too, until I read some of the details.
The Xmegas are "low power" devices. Which means that they do not do TTL I/O. So one of these could never be a drop in replacement for an arduino chip. Sure, you could probably rig up a board that did voltage conversion between the Xmega and the exposed pins, but that would probably run your costs and complexity up to the point where it's no longer worth it.
I wish chip makers in general (and microcontroller makers in particular) would take a page from the FPGA world and separate the IO voltage from the chip supply voltage. That would make them much more flexible.