Right now its pretty much a must-have skill in everyone's rotation for every hero. Even if you just 1-point a skill to stick vuln. As such, it leads to two problems...one, bar bloat for those that don't have it in a convenient rotation skill and have to 1-point a skill just for vuln. Two, if everyone always has vuln at all times then it doesn't really mean anything, it doesn't help differentiate the kits of different heroes.
What I'm suggesting probably wont be popular, but it'll help promote diversity...change vuln (and possibly other binary status procs like Bleed and Weaken) to work on a coefficient: 5% chance per hard point spent in the skill. So if you 1-point your vuln, there's only a 5% chance it will stick vuln properly, before any other coefficients or %-to-procs are checked. If you have a full 20 points in a skill, the vuln will work like it currently does (100% chance, before other factors).
This will help differentiate between heroes, and between builds for a hero. Some builds' rotations will have vuln built into them, some wont, and that can be a factor in overall hero balance. There's always the Omega node to add a chance to proc vuln to every hit too, so that's an alternative path if you want to invest the points in that, but that's not guaranteed uptime like vuln natively in your rotation.
I think anything that promotes more diversity and differentiation in rolespace between heroes is a good thing. I also can imagine a new niche in future gearing for Vuln heroes opening up, like there is for Bleed or Burn heroes.