A great addition would be combo linkers. After the third hit of any combo, switching weapons would make the start a new combo finisher with the second weapon.
I always liked how Bloodborne would allow the weapon to switch style mid combo. This would allow unique combinations depending on the combo linking weapon.
For example, after the third hit with daggers, switching to bow would make you dodge backwards and shoot an arrow, putting distance from the target. If switching to a Great Hammer, it would finish the combo with AoE slam.
You can then start a new combo with the second weapon, and link it to the third weapon, and then again from third weapon to first.
This would also allow the 3 weapons slot to work in synchronicity and the combinations would create unique load outs and play styles.