Yep, it's in the "State of PvP' dev blog under the "to be discussed" section:
" When the Bulwark was released it was looking to fill a niche in PvM to enhance a tanker's ability to help the team when group bossing. As time has gone on, it's clear that the shield has very few limited uses outside of aiding in wilderness protection. This isn't a problem in itself however, in its current format, it gives the player high invulnerability when combined with certain equipment/protection prayers. We would like to discuss any ideas that players may have that allows the shield to have more of a use outside of PvP and also talk about reducing its effectiveness in PvP situations. "
OSRS Mage Tank.
Believe magic to only be for support? Think again. It's just as valid of a Pking style as melee and range is.