I don't think it stacks per spell, Sev. Not sure if that's what you meant?
Wyrmskin Gloves Slow, if it procs before the last one evaporated, will replace the previous. Where we run into abuse is that each effect will stack with a different spell that does the same thing. So Reg's Snare will stack with UB's Diseased claws will stack with Wyrmskin Gloves. I don't think two players with Wyrmskin can stack that effect, but it doesn't really matter, because it will endlessly replace before the timer runs out.
I was thinking in this thread that the best solution would be to get back under the hood and rewire spells so that they have no effect while similar spells are in place. Take out replacement and you've ended stunlocking, shield-chaining, and slow-chaining and introduced some micro