I think the original dual wield system was fine, and I do get what you're saying with the new features of it, I find those specific ones unnecessary, and would much rather have a system more similar to Halo 3's system. To be honest I don't get what you're saying with them being bad by themselves. Plasma Rifle is a great and personal favorite weapon of mine, and the SMG does fine as well.
They're very similar, plasma rifle, SMG, spiker, ect; good power and fire rate, low range. Works out fine. By themselves I've used them, and same when they're dual wielded. Same goes with the magnum and mauler.
Dual wielding swords is a terrible idea. Sure, it'd be cool for Machinima, appearance, which would quickly be worn out anyway, but the game mechanics would be all screwed up with it. The same exact thing goes for the energy spike (I believe it's called), appearance is cool, mechanics would be screwed up.
They should be as good as just any weapon that is there, AR, BR/DMR, Carbine/Needle Rifle, ect, but when you dual wield it, the reticle should become larger, decreasing accuracy for power. This all depends on bloom being absent however, which I'm not suggesting nor disagreeing with.
The Jackal Shield idea has very similar thoughts although it works a lot differently. It could be interesting, a bit unoriginal such as MW2, but not the worst idea. It'd be hard to do, considering jackal's size and their shields, providing very little cover. But the whole energy battery concept is interesting. It could be cool, but not the best choice and I won't be too excited, nor will I complain if it's implemented in, if dual wield is in at all.