[smalley]

VISA isn't for qualifying chips as much as it is for debugging chips including customer returns. Long ago access to limited versions of the signals was given to some customers under NDA and customers had the ability to set customer fuses which would prevent Intel from unlocking the debug features. There's also an unsupressable "debug enabled" bit hardwire to a lot of these functions if I remember so the parent system can always see if somebody turned on the debug functions. Turning on debug functions also usually had the effect of disabling/corrupting important key material.

This said, its basically a giant signal mux system run into a main block, you'd be pretty limited on what preselected signals are available at a time. People were also reasonably careful not to give entire busses of signals at once.