I'd think dual wielding would be an interesting addition to the game, so I would like to share my thoughts on how it might work.

I believe that dual wielding would only work on guns. This would gives guns more diversity and options.

When entering the dual wielding "stance" the user loses the ability to block, shield charge, dash, use charge attacks, and would have a very slight damage reduction, but not that much.
When dual wielding, m2 is rebound to the second gun.

To set up dual wielding, the user would select a gun and then another gun in his/her arsenal. The first gun picked will trigger the other gun to appear, but not visa versa. This would allow the user to have multiple combinations using weapons already bound. Lets say you have guns 1, 2, and 3. You could select gun 1 and gun 2, then, select gun 3 and gun 1, even though it would be already being used. When hovering over a linked weapon in the arsenal, it would highlight it and the linked gun a certain color. So, for example, gun 1 would be a blue connection, while gun 3 would have an orange connection.

I think a good button to map the dual wielding trigger to is the middle mouse button, or shift and the middle mouse button, so you could switch between single and dual wielding quickly. However, you can move while switching, but it leave you vulnerable because, while switching, you can't attack or defend, so positioning and timing are key.

I hope you enjoyed my ideas, and please, tell me what you should be changed to optimize this.