A two weapon fighting thought

[Mortuum]

What happens if we ditch the old rules for two weapon fighting and replace them with something like the following?

Dual Weapon Attack

You can attack with two weapons at the same time in place of any normal attack.
When you do, make a single attack roll. On a hit, you deal damage with both weapons, adding your strength modifier to damage for your primary hand weapon and half your strength modifier to damage for your off-hand weapon as normal. This counts as a single hit, so don't stack typed bonuses to damage from the different weapons or apply precision damage more than once.

It's difficult to apply as much force when attacking with two weapons unless the weapons are light. Unless the weapon in your primary hand is a light weapon, take a -1 penalty to damage when attacking with both weapons. If your off-hand weapon or both of your weapons are not light, take a -2 penalty instead.

When you use power attack, add both the full bonus to damage from the weapon in your primary hand and the halved bonus to damage from the weapon in your off-hand.

If you score a critical hit, multiply the damage from each weapon by its critical multiplier as normal.
If you threaten a critical hit for one weapon, but not the other, roll to confirm the threat for that weapon alone and do not multiply the damage from the other if you succeed. If you threaten a critical hit with both weapons, make a single confirmation roll for both.

If it's unclear which weapon is dealing extra damage, but it still makes a difference, (such as when you sneak attack with a lethal weapon in one hand and a non-lethal weapon in the other), the extra damage is dealt with the weapon in your primary hand.

Anybody can attempt a dual weapon attack, but unless they have Dual Weapon Attack Proficiency, the roll is made at a -4 penalty, as though they were non-proficient with one or both of the weapons. Classes that start out proficient with all martial weapons are considered proficient with dual weapon attacks. For everybody else, it costs a feat.

Crossbows

Spoiler:

If you dual attack with crossbows, you do not take the usual penalty to damage for dual attacking. However, the penalty to attack rolls for attacking with a crossbow held in one hand applies. It stacks with itself and everything in the game. You cannot effectively wield a heavy crossbow in your off-hand at all.

Conjoined Weapons

Spoiler:

Conjoined weapons replace double weapons and the double crossbow in this system. Rather than having their own stat-line, double weapons are just pairs of standard weapons stuck together.

Their weight is the sum of the weights of their component weapons and their cost is the sum of the costs of the component weapons +50 GP.

If you wield one of a pair of conjoined weapons, you must also wield the other. If you are disarmed of one, you drop both, but if one weapon is broken or destroyed, the other is unaffected.

When you attack with a conjoined weapons, you can either use one of the weapons as though you were wielding it in two hands or make a dual weapon attack.

Conjoined weapons can be enhanced individually, but they are more commonly made as paired magic weapons

Paired Magic Weapons

Spoiler:

Paired weapons share a single enhancement bonus and and any special properties they might have. Their price is the cost of both base weapons plus the cost of adding their bonus and properties to a single weapon.

If you use a paired magic weapon and you aren't wielding the other weapon in the pair, treat it as a masterwork weapon. If you wield both at the same time, add all of the pair's bonuses and properties to attacks made with either weapon.

[LostSoul]

This would completely hose rogues an already low power class.

[Mortuum]

True, they wouldn't thank me for it, but if it's a choice between TWF and sucking, they're too dependant on TWF anyway. It's an inferior choice for pretty much everybody else (even rangers) so making it a viable fighting style in general and then somehow fixing rogues, who, as you say, are low tier anyway, seems like a good idea.