I dunno if the features are that relevant to an arduino-like product. It's a form of multiprocessing, which is a whole huge can of worms from a software development perspective.
Two good issues.
The XMEGA gives an obvious upgrade path when an application is now too demanding for an ATmega but perhaps cannot justify the cost, complexity or power consumption of a larger processor. I have several applications where going to an XMEGA will save me a cmplete re-write, and lsave me from learning YANP - Yet Another New Processor.
If you were to ignore the new features, you get a MEGA-AVR with lots more I/O flexibility. But managing an event system and using it with DMA are not for the faint hearted.
But an XMEGA Arduino? Something using an XMEGA is going to be very un-Arduino like!
The Geek