Dual Wielding
From a code perspective there is some difficulty (mostly that wielding two things is outside of the currently allowed (only a single weapon slot, etc.), it would break weapon swapping (a, b), etc.)
From a balance perspective; it'd be stronger than a 2H weapon and allow two brands, but need more Enchant Weapons to get to maximum Armour penetration (also 2x15 [two double swords] might not pierce armour as well as 1x19 [Triple Sword]). In general, even with skills balanced to make it harder to reach mindelay (or a higher mindelay than single wield); it'd probably GENERALLY be more powerful, but still less so than Blade Hands and Dragon Form (which can break 30 base easily (15/15 stats, blade hands and 9 UC is 30 base, but slow); 27 UC 15/15 stats and blades is 48 base.