
Prerequisite: Requires a Strength score of 10 or higher. Warforged or Construct.
Your ability to adjust to changing circumstances has been greatly increased and you have learned to modify your Warforged Integrated Protection much more quickly.
- If you are not already proficient, you gain proficiency in Medium Armor for the purposes of adopting Composite Plating.
- You can choose to adjust your Warforged Integrated Protection as an action, rather than after a long rest.
NOTE: Class or ability restrictions such as a druid's inability to wear metal or any monk ability dependent upon unarmored movement still apply.

Seems a bit strong since the medium armor mastery feat requires you to be proficient with light armors. I'd love to take this for my wizard warforged but that'd give me 5AC(that scales up on later levels with proficiency) at level 4 and the ability to adjust integrated protection as an action. Maybe it should require light armor proficiency or scale up the proficiency you have. For example if you have no armor proficiency you get light armor proficiency, when you have light it becomes medium and when you have medium it becomes heavy armor proficiency.
But otherwise a cool feat!
I agree with you on that. You can even phrase it as "You gain proficiency with armor one class heavier than you already are proficient with, if you aren't proficient with armor, you are now proficient with Light Armor."
I would also make it take a minute to switch around all those armor plating, not just 6 seconds.