Two-weapon fighting in Dungeons & Dragons has almost always been a bad idea. I do not think it was even possible in Basic (barring houserules), but according to 2nd Edition's Combat & Tactics you could try attack with two weapons, you just took a -2 to the first attack and a -4 to the second. 3rd Edition kind of kept this model, starting you out at a whopping -6 and -10 to attack, which could be reduced to -2 and -2 through the use of lighter weapons and feats.
4th Edition made it more universally applicable through the use of feats and its power system. The Two-Weapon Fighting feat gave you a +1 bonus to damage when you made attacks while wielding two weapons, I guess assuming that you worked the other one in there at some point. Simple, to the point, and stacked with Weapon Focus, though understandably too simple for some, which is why it was nice that several classes--namely barbarians, fighters, and rangers--had access to at-will multi-attack powers (though many higher level attack powers let you hit multiple things, too).
The current take on it in Next is that you have to be wielding a light weapon, you take a -2 penalty to both attack rolls, and you have to use the light weapon's damage die for both attacks. Oh, you also do not get to add any bonuses. So, as an example, let us say that a fighter with a Strength of 16 wants to hit an orc with a longsword and short sword: she makes both attacks at a net +2, and if she hits both times will deal an average of 7 damage.
What if the fighter just ditches the short sword for a shield? She makes her one attack at a +4, deals an average of 7.5 damage, and has a slightly improved Armor Class. Even if she goes with the short sword her damage is only reduced by a half-point, but she is still way more accurate. If she decides to on a full-offensive and pulls out a greatsword? Her attack bonus still stays at +4, but damage improves to 9.5.
Of course none of this assumes feats, of which three out of the Two-Weapon Fighter specialty are directly applicable:
- Dual Wielding lets you use any one-handed weapon when making your double-attack, which can improve the average damage from 7 to 9 (assuming two longswords, here). You still have the penalty though, so you are spending a feat to make less accurate, slightly less damaging attacks.
- Two-Weapon Defense gives you a slight Armor Class boost, which means that with Dual Wielding you are now doing better-than-longsword damage, with the same Armor Class, but are still less accurate.
- Eventually you can get Two-Weapon Strike, which lets you make one attack with advantage. This is a pretty good payoff because you are also making the attack at your full bonus, and you get to add damage bonuses. The drawback is that you have to spend a feat on Dual Wielding and wait until 9th-level.
My proposal was to allow a character with two weapons that attacks the same target to roll both damage dice, keep the highest result, and add her damage bonus. This makes it so that you get more reliable damage, without exceeding what a character with one weapon can do (or doing more than a character with a two-hander). You could do this as part of a single attack roll, or require that both attacks hit in order to gain the benefit (which has the advantage that the dual-wielder gets another chance at landing an attack, though she will not always get to roll extra dice).
The problem is that this only works against a single target. What about hitting multiple targets? In this case I was thinking of a mechanic where the character can divvy up damage to two or more targets, which would again prevent the dual-wielder from out-damaging the two-hander. This could also require the use of Martial Damage Dice, like the monk's Flurry of Blows, as the benefit is that the fighter gets to make extra attacks to stack damage, instead of rolling multiple dice and taking the best result.
As for the sorcerer and warlock, I still see no reason why the dragon-sorcerer cannot be a heavy-hitting melee-ish spellcaster type. I really dug the sorcerer mechanic, and hope that future iterations retain the "manifest traits as you cast more spells" shtick. Frankly if they are going to make a warrior mage, why not make a warmage tradition?