That optional rule for Structure Checks and Stunned is very intriguing to me. I assume it playtested fairly well? Did you encounter any surprising side effects as a result of players being able to use it?
Also, I have a quick question about the additional structure check that Stunned players can choose to take - I assume this second structure check results in the same consequences as usual? For example, let's say I'm a player mech and I've just lost my second Structure. I roll 2d6, getting both 1s. Per this rule, I become Stunned and I roll on the System Trauma result. My next turn comes around, and I take a single quick action. I then choose to attempt another structure check. I roll 2d6, getting a 4 and a 5. This means I take the System Trauma result, and then must roll 1d6 for that as well, destroying a weapon or system per this result. I may then take another quick action. Is this all correct?