I didn’t want to create a new thread for a simple question.
Is Eric’s picking motion rotational? I’m watching some clips and to me it looks much like wrist deviation. Am I mistaken/deceived by the footage angles? If I remember correctly, CtC claims that Yngwie uses rotation but I don’t remember any similar deconstruction of Eric’s picking mechanics.
All good, seems like a distinct question so I think a new thread seems to make sense in this case!
Have you seen our Cascade seminar, or the EJ material in the Pickslanting Primer? Just want to make sure it’s clear we do have lots of material on Eric’s technique 
If you’ve seen that stuff but still have questions on the specifics of his picking mechanic Troy can speak to this in more detail.
Brendan ruined my plan to go under the radar with this question.
Yes, I’ve seen the Cascade seminar but I don’t think this particular detail was discussed there. Most of the footage in the Cascade was taken from the Austin City Limits performance. I also checked some random YouTube clips of him playing (some from the same concert).
To my untrained eye, his picking motion looks a lot like wrist deviation when he goes into fast dwps. Now, I should note that I don’t really perceive Yngwies’s picking as rotational either, so perhaps I simply don’t know what to look for 
I believe it is for two reasons: one being that it appears that way to me although like most it’s probably a combination of more than one mechanic. It looks like rotation mostly with a tad of deviation. Secondly, I recall Troy mentioning that DWPS playing usually lends itself naturally to this motion mechanic.
That’s what it appears to be, with bits of finger movement in there, as Eric has mentioned on occasion. There is probably less finger movement in there than has been popularly attributed to him, but there is certainly some, depending on the phrase or perhaps the strings he is playing on. @Tom_Gilroy has looked at this a bit and may have further thoughts.
Eric doesn’t usually play with short sleeves so it’s harder to say how much forearm is involved, but it doesn’t really look like a forearm movement.
I’ve said this before, I’ll say it again: when in doubt, look at the path the pick is traveling and ask what joints can create that movement. If the pick travels parallel to the pickups, the forearm can’t do that - not by itself anyway.