Motor On wrote in post #16755522
And the 580 extends farther forward, as long as it's not stored in a bag while attached to the hotshoe,
with handling care I don't see it being an issue. Let it bounce around on your side all day or stuff it in a bag that then has a load shift on top of it while you're in route, and it could be an issue.
Anything I've seen commercially available goes straight up and has some minor articulation, like a less flexible speedlite to light stand adapter, so the leverage is just on a different plane.
And of course there's always the damage that running 2 cameras at once will do to the free space remaining on the hard drive graphic.
I have the tripod mount and could mount it directly above the hotshoe, but with the wide angle of the GoPro and the 70-200 f4L length, you get the lens in the view. It also raises it up another 1 & 1/4" above bore which isn't a big deal, really, but I would like to keep it as close as I can.
I have a couple of off-body flash frames I could use, but they add weight and bulk...
Hmm... not going until Saturday, so I have time to experiment.
And just to prove that there is nothing new under the sun, a quick search turns up thousands of folks who thought of this before me. 