http://youtu.be/qf5LjypWZNs?t=7m24s

According to this.

Bad idea. This actually means everyone will just look like a hodgepodge of various armors. No uniforms for anyone. Our guild WAS going to have a PvP uniform which would have been a costume so you'd always know when our members were around (since not all of us will be using the same type of armor) so what, Maria, are we supposed to do now? Again we are being boxed in and our fun is being limited for no real reason. All the person's appearance will tell another player is the type of armor they are wearing. That's it. It's not going to indicate anything truly vital like what class they are, what skills they have slotted or enchantments they have active at the time.

Give us costumes in Cyrodiil please. Even if we POOF out of them suddenly when we engage an enemy, allow them to at least be worn and then put back on after combat...

Can't have costumes. PVP'ers can't stand not knowing what your armor is from a distance. Their entire strategy is based on your choice of fashion. If they lose, it's because they thought you were wearing fall fashion instead of summer. Sad, but that's the way it is.

First, you are allowed to wear your costumes over your armor in PvE. That is brilliant. LOVE IT!

As far as pvp, she was pretty clear why you can not do it. Seems logical to me.

At the least it should be like-for-like; plate costume items for plate wearers, cloth for cloth, etc.

Having talked to a small number of successful PvP players in WoW the first thing they look for is health and mana bars, this tells you at a glance the approx level of gear they have equipped. The art of the gear was secondary. Any summoned creatures would not change, spells effects could not be changed, etc.

There's no "What!? I got one -shotted by a guy in a Tier 1 set!!!". It's "omg, he had 500k health and mana, and stun locked me for the duration".

After playing for a while after transmogrification was released it's refreshing to see what people can do with a costume tab. PvP players better be checking health bars long before admiring the other guys gear especially when life is on the line.