I already heard some rumours that the AVR ONE! can also be used to debug AT(X)mega in near future. And if you look at the newest AVR Studio release 4.15 you can find the following:
Support for the new AVR ONE! on-chip debugging and programming tool. Introducing Live debug that enables you to attach/detach to running processes (AVR ONE! feature only)
Has anyone further information about this? Will there be something like a trace?