Will the limp speed be upgraded for this? Right now the limp is so slow you might as well not be moving at all. Even catastrophic engine damage only gets you a -50%, the limp gets you like -99.9% speed.
Also, if this is going to be for legs only (for now)... and it can't be repaired? This sounds like it would do for mechs what the turret and hull is for tanks - just a bigger reason to shoot it and only it above anything else. You can beat up and break off side torsos of a good mech player, but if he can't repair his leg armor, you're better off shooting his legs exclusively forcing him to buy a new mech.
Regardless of your stance on legs, I don't think we need more reasons to shoot them.