Below the line,
Think of what the autobrakes are giving you (decel rates), and what the effect of using reverse is ... does it change the decel rate ?
Autobrakes LOW 1.7m/s². .Autobrakes MED 3.0m/s². .Autobrakes MAX 6.0m/s²
So what to you achieve using asymmetric reverse in terms of decl rates, nothing. You actually will increase directional control problems, and increase brake wear (the carbon brakes increase wear when operated below 250 ºC) which is typical when reverse is used.
In an emergency the best option would be so set the park brake and lock the wheels up before thinking of going for reverse, at least you have a better chance of staying on the runway.
Z