I like the idea of legendary gear being able to change the way characters play and I hope new gear is added to enhance the grind and add depth to gameplay. With that I have a couple ideas to add said depth.
I think the sprinting melee attacks that a few characters have couple be expanded upon.
Attikus could have knockback and damage added to his sprinting melee proportionate to his movement speed. The gear could also increase sprint speed for every second in a sprint. Mental Mars suggested it be called Bulldozer. If you had a nice runway and team help in the form of movement speed, you could take out a wave, boss or enemy battleborn much quicker.
Mellka could have a lengthen slide that could allow her to fire her gun while sliding in at someone and maybe gives her some damage reduction or cc invulnerability while she does it making her much more slippery.
Deande’s could help her soften up enemies by adding a slow, amplified damage or reduced damage taken from target. Maybe it could also add a roundhouse possibly inverted(a la Chun LI).