I was recently talking with Aktorin about having hand-held shields. I think it should be an external HP source; AKA a second health bar which absorbs damage until destroyed. After the shield's destroyed, your main HP is now exposed to attacks. A mech should only be allowed to have one shield equipped at a time. It'd be cool (if shields are added) if the shields were customized to certain attack types.
Don't understand? Allow me to show you:
Physical
-Reduces physical damage by 10-30% (chance based)
-Immune to physical resistance drain
-Increased heat gained/ energy drained from opponent attacks
Heat
-Reduces explosive damage by 10-30% (chance based)
-No heat damage taken from opponent attacks
-Extra damage taken from electric attacks
Energy
-Reduces electric damage by 10-30% (chance based)
-No energy drained from opponent attacks
-Extra damage taken from explosive attacks
Omni-Resister
-No external health or damage-type reduction
-Immune to debuff effects

As for DoT effects, I really like that idea as well. Never really thought of it until reading this post. Here's the effects I thought of:
Oxidization (lasts 1 turn)
-Unable to move (only moves by being knocked back or teleporting)
-Charge and Grappling Hook impaired
-Positive resistance reduced to 0
--Oxidizing weapons should only have 1 use and have high resource consumption with low damage. Weight should be above 70kg
Static Charge (lasts 2 turns)
-Taking electrical damage every turn (energy drained every turn as well)
-Energy regeneration reduced
-Damages self when an energy-consuming weapon is used
-Electric weapons have reduced damage
-Teleport impaired
-Drone sabotaged (deactivates for 2 turns)
--Only one stack of static charge can be active at a time. Wear-Off time, however, can be reset by using a shock weapon
--Over 70 weight, and large energy consumption
Burning (lasts 2 turns)
-Taking explosive damage every turn (heat added every turn as well)
-Cooldown greatly reduced
-Melted Armor (attacks ignore defense)
--Stacks up to 2. Wear-Off time is reset when a second stack is added
--Over 70 weight, and large heat consumption
Leaking (lasts 1 turn)
-Taking physical damage every turn
-Damages self when any action (besides drone, kit, and shield) is taken
-Shredded (positive resistance is flipped to negative resistance; increased damage taken)
--Stacks up to 3. Wear-Off time is reset when another stack is applied
--Over 90 weight, and melee abilities only
Stun (lasts 1 turn)
-Loses turn
-Stun cannot be applied for the next 2 turns
-50% chance to apply
--Over 60 weight
--Great for hammers, if hammers are added as well

Okay, I'm done. *phew*

Voted yes.

DoT would be a great addition. Poison or corrosive substance.

I think this was suggested way, way back but never implemented.