I've never made any Samurai Plate for any of my chars, so I'm not familiar with it's base properties, etc. But - I am curious as to your logic... Why would a Mage not wear Samurai Plate with Mage Armor on it?
Because it's gobbling up a property slot for no reason compared to just wearing leather.
Right now the Mage Armor property is just sort of dangling out there like a vestigial organ, unwanted by anyone. Letting an NPC remove it for a fee was a sloppy kludge of a solution. There are ways it could have been accomodated (not having it remove the LMC/stam bonuses from armor it appears on and then making other changes to balance this) but by far we would have been better off if it had just gone away completely.
Here's what I'd do, just because:
* Mage Armor goes away, everything becomes medable.
* Inherent LMC on armor goes away to balance this out.
* Metal/stone armor keeps stamina protection bonuses.
* Leather/leaf armor gets some other mage-related bonus.
* Studded/bone armor gets a little of both.
I'm not going to try to pick the mage-related bonus for leather right now because it will just derail the thread. In an imaginary world where I was running things I'd take a few weeks to shake it out on Test Center and pick something balanced. But yeah this business where armor can be spawned with an item property literally nobody wants, and then you go have an NPC remove it? Sloppy.