Well, it's a fairly rare form of tapping and more or less a novelty. But, I'd argue there are actually a few guitarists who use it. Adam Fulara and Stanley Jordan both play exclusively 8-finger tapping. However, I think the confusion stems from the myth that 8-finger tapping is used in runs or something...and that's not the case. Most of the 8-finger tapping that I've observed by guitarists such as those I mentioned above follows something like this: One hand taps the melody or solo, while the other hand does walking basslines, chords, etc. It is very rare that both hands would be used in conjunction, however, to pull off 8-fingered legatto-style runs or whatever.