Shield up currently gets no use because parry and oak stance are simply much better in terms of offense and defense
The extra defensive weight is nice, but the fact that openings don't tick downwards slightly when attacked (like oak stance) means that parry is the better alternative if you are deciding to go MC-based. And at that point, there is no reason to wear a shield.
Sword damage is currently much worse than the 2 handed weapons, and so I feel that shield stance could be given the same defensive traits as oak stance, only without the weight reduction on attacks. If this change was made, high-MC with low-UA builds would be much more viable in PVP and PVE.
Right now it is not worth camping shield stance, but if it was made more tanky in the way I'm suggesting, I could see the play-style catching on again.