I would like to see a rule for two weapons to the effect: choose one weapon and roll its attack dice and use its passive abilities. Surges may be spent on either weapons effects. With the exception that the 2nd weapon must also be able to hit the target (no spending melee surges on a ranged attack, or reach etc.)

That would also be my first idea to simply allow surges to be spent on either weapon abilities.

There is already a class which benefits from Duel weapons. I can't remember which one, i'd have to look.

But the player is allowed to use surge abilities form both weapons. If you start adding all kinds of weird duel weapon house rules you may break this class.

Skirmisher from Shadow of Nerekhall is a reasonably strong warrior class which specializes in dual-wielding.