Interesting,
is this the skill? Or is there another upgrade? It doesn't mention anything about reload speed, but I guess the speed effect just improves all animations? That plus
Embrace the Void could make quick-reload Voidwalker builds a ton of fun. I'm putting it on my list along with Chain of Woe Gunslingers and War Machine Defenders as a viable gimmick Thorn build.
And yeah... if by "not top viable" you mean raid gear then no, it's not raid gear. You can't control the stats or mods that drop on you for raid gear and thus can't build around it (without working backwards). Eclipse Maw is from the Warlock vendor.
Feel free to add me; best thing to do is just watch this thread for me to ask for people to do it, I'll be home at about 7:30PM EST and might squeeze one in before raiding at 9. If you get people to help before that point then by all means go for it.