OK, a little idea on the whole double-bar thing that occurred to me:
Allow the option to not slot a second weapon, but still access the second bar. Treat it as one continuous bar of 10 slots, even though you have to swap between them to actually hit the buttons (due to the limitations of making them workable with a game controller).
The downside would be losing access to a second weapon. For example, no bow backbar with dual wield or 2H frontbar, or lightning staff backbar with flame staff front bar, etc. No Maelstrom backbar weapon for that set bonus while also getting another set bonus when swapped to the front bar. Etc.
The upside is that you eliminate the "double-barring" needed for some skills. No losing a summoned pet when swapping bars. Passive buffs are always in effect, without having to slot them twice. Etc.
You might have to drop the ultimate from the backbar, or require that it's the same as the frontbar. Not sure where that'd fall in the balance of things.
And the interface wouldn't need any extra complexity. Just take off your second weapon if you want to treat all the front and back skill slots as one continuous bar.
There are reasonable reasons to want to take advantage of multiple weapons (eg: healer wanting to apply debuffs from a destruction staff), but there are also reasonable approaches that don't need an extra weapon, but would benefit greatly from simplifying the slotting situation.
I'm not sure how this would impact the overall balance of the game. There are far too many combinations to think that I could casually judge what impact this would have. But, while this would definitely give some advantages in some areas (but not in others, where it is reasonable to want to stay with the two-weapon build), my initial reaction is thinking that they would be balanced by the losses, and that it would mostly allow more creative diversity in build design.
Anyway, it's a thought. Maybe someone can explain why it's utterly broken. Maybe the devs will give it a shake to see how it works out.