This is all good, till you get into organized PvP. Jinx, when used with CoE, replaces all curses with the new "Jinx:Curse of Elements" debuff. This means that you put up CoEx on a rogue and CoT on a mage and then try to nuke down the priest with CoE, all other curses are removed, and if CoE is removed for whatever reason on the priest (thru remove or the priest dieing), the other curses do not return unless recast. This makes CoE a severe liability in any organized pvp with casters/healer/or melee on the other side (yeah, so basically all organized pvp -_-)
Curses are a big part of what allows locks to function well in pvp, on live and in cata, from what I've seen and done. CoEx on melee is huge if you can't apply it or it gets removed when you switch targets. CoT on healers and casters is the difference between winning and losing, aswell as the new CoW with melee (basically CoT but stronger). CoE is still needed on resistances and kill target.
Only allowing the dps curse in pve also affects us. If there is any raid boss in cata that needs CoT (healing fights come to mind), CoW (if no body else brings the debuff and the fight is a heavy melee fight), or CoEx (any kiting fight) the only way to do this is either drop magic dmg and remove coe (or not put it up) or hope someone else brings one of the debuffs to apply themselves. I've never seen any class take a talent that reduces utility like this (I know shadow priest... I know). It would be like a mage only allowed to use the armor of their spec, or a talent in arms that allowed bladestorm to do full dmg on a single target again (aswell as all other targets in 40yrds) but then removed all snares/slows (or in reverse, gap closers).
With the way the Jinx talent affects CoE, it basically either removes CoE from any pvp (except bg pugs) or remove all other curses from all pvp, either way, this talent cripples our pvp (and pve utility).
This could easily be fixed if the Jinx debuff (the one that gets spread) is not considered a curse casted by the warlock. Right now, you are only allowed one curse per target per warlock, and this makes sense. Jinx though is currently considered a curse casted by the warlock. If this was changed to be, similar to haunt, an ability casted by the person it is used on, this would fix all that is wrong with it.
To those that do not know, when you are healed by the haunt spell, it is considered a healing spell casted by the person it is returned from. If the Jinx effect is considered a curse spell applied by the person it is casted on, this would allow jinx to be applied while other curses are used.
The only problem I can see with this, is if it was used on another warlock to remove his curses, and if that happens, just make jinx a magic effect that is replied when dispelled. CoE on the main target would still be a curse, as is it now, but the Jinx effect could be considered a magic debuff. This would keep it up basically 100% as long as the curse is still on the main target and they are in range of each other (same as now) and allow 1 curse per warlock per target as it should be.