We don't need an NPC shop for materials, we need a trading house or whatever for them (http://forums.spiralknights.com/en/node/2043). The players supply more than enough materials. The problem is we don't have anywhere reliable that we can sell them other than standing around all day saying "buy this, selling that".

Also something like this would just kill the market for player trading. People would have to cut their prices in half at least to attempt to compete against the NPCs. Now some items are near impossible to find so I hear (trojan horseshoes?) but not so many that we'd need an easy way out like this (plus anyone who finds a trojan horseshoe wouldn't be able to snag a big sell anymore).