Since he is insisting on mithral I would hazard a guess he is looking towards getting something that can be enchanted with magical abilities since anything made of mithral is automatically "masterwork".
Do not let him end up with a poor man's solution to getting masterwork armor to enchant - and don't let him bypass the "body slots" restriction.
Oh, I won't. If he wants 'em to have armor abilities, it's gotta provide an Armor bonus, and it'll take up the boots slot. And that party doesn't have a dedicated crafter anymore. So, to do that he'd need to find and convince someone who can do that kind of thing to do it for him.