Itemization

[Skandranon]

Of those two items, the Caster helm is worth around +27 dps to a 3.0 second spell talented to 2.5 seconds (more for elemental shaman, less for untalented spells). The Rogue one is worth around +6 dps plus specials (very generously another 6 dps) and the hit/crit/dodge chance. I'd rather have the 27, thanks.

Keep in mind that rogue damage also scales up by weapon. Rogues aren't supposed to get the same dps off the same equipment as casters; Skyshroud Leggings offers +11 dps and Shadowcraft Pants offers only +2.5, but no one disputes that they belong in the same category. Proportionately, the gap begins to close as +damage is required to stack higher.

It's also very possible to build caster helms with a wide stat spread - using six entries as that Rogue one does could give something like 1% spell hit, 1% spell crit, +25 Int, +25 Stam, +30 damage/healing and +30 to a random spell school (or something near that, I haven't calculated the cost).
[right][snapback]88849[/snapback][/right]

Recognized. However, you only need a few such items for PvE. Once you've gotten around 3k/6k, the int and stam become, as they've started to become on current items, essentially meaningless. 1% spell crit and 1% spell hit spread things out a little, but again, there's only so much spell hit you can use. Rogue items can replace +tohit with dodge or an incremental increase in previous stats; casters have to pile damage.

Splitting the damage between +to all and +to specific works, too. The problem is that you can't reasonably design such equipment and expect that everyone will wear it. There will, for example, be three mage helms: each with +40 some odd to all and +30 to either frost, fire, or arcane. Even assuming the ZG token system is reused and you get to pick, you're essentially barred from respeccing once you've gotten the first item of your set. It's a restriction on your level of flexibility which isn't acceptable, and for that reason I don't expect Blizzard to pursue this path.