Yes, back in BC when bears almost became 'real' tanks (there were still encounters that were nigh-untankable by anything but a warrior vs. one gimmick fight that required one of each kind) there was some bear-specific gear. It was widely reviled because A) there was usually only one piece (or fewer!) per slot per tier and B) they still clogged loot tables, not least because many raiding guilds had no feral tanks. And even with the existence of bear leather, the itemization was horrible; see crit immunity.

'Tis a heavier argument, IMO, to add a category of gear than it is to remove one. If brewmasters can use rogue leather (even if they have different stat priorities) then they should be balanced to do so with the expectation that they get their defensive stats from gems, enchants, and reforging, the way bears do now.

If you've got enough space in your drop tables that there's space for pure tanking leather, then you've got space for multiple variations of agility DPS leather, including one that has stats that a leather tank can appreciate; this allows you to have, say, one piece that's ideal for subtlety, assassination, feral, and brewmaster with another that's better for combat, windwalker, and guardian, and while you'd prefer the 'ideal' piece the other one will work, if not as well.