Warforged / Bladeforged don't have a "medium armor" feat option.
When I researched why, I found out that this is because the Mithral feat is actually *supposed to be* the Medium armor option, since 'Forged folks automatically have light armor on via the Composite Body feat.
It seems like it would be easiest to just change the code from "consider Mithral Body as LIGHT armor" to "consider Mithral Body as MEDIUM armor" (as far as PRR/MRR are concerned).
But if that is unappealing to developers, why not just add another feat for WF that is medium armor?
Byeshk Body would rock.