Hidden Debug Mode in AMD Processors

Almost certainly not; the features are modeled after the DRx hardware debug registers. You can't access them from userland, and the debug registers are already virtualized.

I haven't been able to read the article either but, from teasing apart the /. comments, it appears that they are extensions to the normal debugging support and aren't an immediate cause for concern.

(If it's just a way to trigger a breakpoint based on the contents of a write, then that's only a subset of the documented capability.)

Probably not, although I couldn't tell for sure at this moment. It's certainly a lot cooler debugging feature in relation to Intel chips.