While this would be amazing and people have been asking for it, one of the latest live letters gave us this:

Quote Originally Posted by Bayohne View Post
Q18: Do you have plans to implement a feature, such as a book that records items you have obtained once, and you can drop that item but still use it for glamour? With this feature it’ll free up the inventory space.

A18: Yoshida: We have no plans for this. We would increase the inventory space if this was possible.
So it looks like there were plans for it once, but those plans have been stalled indefinitely and currently there no plans for a armour/weapon log of sorts.