I guess specifically I’m talking power chords, as I’m sure the technique may be a bit different as you start to add more strings into the equation. But is the idea to not create an escape motion at all and to just move the pick side to side within the plane of the strings (aka no pickslant)? Edge picking also seems a bit awkward once you add in more strings, so should the pick just be kept parallel the entire time? This seems to me to be the most intuitive way to tremolo pick chords, although the lack of edgepicking introduces more resistance from the strings and messes with me at higher speeds because I’ll find the pick slipping out of my grip at times.
What genre are we talking about? Funk / flamenco, kind of? If that’s the case, then yeah, I would say you don’t want any escape, and ideally, very little edge picking.
If this is for something like metal, I would argue that you would rarely, if ever, trem pick a chord.
Here’s a good video on it, he actually references Troy at the start of the video! Looks like he is using a floating wrist/forearm USX setup 
Thought I would find another video to see if this setup is commonplace in black metal and Charles Hedger of Mayhem seems to use a similar mechanic:
It kinda reminds me of the tremolo you see in Gypsy Jazz in a lot of ways, Troy put Joscho’s tremolo under the magnet if you want a good close up of what’s happening:
All that being said, I’m sure there must be some examples of black metal guys using elbow and wrist but this could be a good starting point 
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Whatever this guy is doing (should start at 5:08, a good blend of single string playing and tremolo chords)
It isn’t filmed from such a helpful angle as the other vid above but it does look like he adds a bit more wrist flexion for the multi string tremolo in the gypsy manner.
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Yeah, Ihsahn uses flexed forearm rotation (gypsy jazz/EVH style) with maybe a bit of wrist thrown in. You can see it better in this video at 2:40:
I do it forearm and wrist blend like the above videos show.
I don’t tend to think about edge picking with this, but I know I add a little because I used to find my up-strums would get a little jammed. I just adjusted my grip by feel to get it working.