A very good and complete writeup of an uncommon piece of equipment. Does the Kellerhadrin Plant fiber ever wear out or degrade? I'm sure the suits are broken far before then, but it seems a releveant qestion. If the plants are still alive when they are used you might even have to water your armor.
A note: with its strong foundation in dealing with knowledge, archives etc., the Ark will have a very strong handle on noblemen. Why?
*You need to legitimate your claim to a title. Of course there are documents to prove your right. Kept by an Archivist. Of the Ark.
*You need novel weaponry to defeat your foe. It was invented recently. By a scholar of the Ark.
*You need religious support to motivate your troops. Priests of the Ark can do that. (just look at the Investiture Controversy in the 11th-12th century for a conflict between priesthood and nobility).
*You need competent magistrates to run your realm properly. Of course they are members of the Ark.
Simply denying services will calm many an uppity noble quite swiftly. If the Ark withdraws its members from a realm, it will soon become a hillbilly backwater - especially considering that intellectuals will drain from there to realms where the Ark maintains presence.