Will there be collision detection? Or will everyone be able to run through everyone in pvp battles, rendering the "heavy warrior front line" useless.

The warriors would block everyone elses path from getting through to kill the archers/healers if there is collision detection, like a Total War mechanic.

Also, will we be able to use mounts in PvP?

I know DDO had collision detection. It was great, it created opportunity for new strategies. So, I know it's possible. Whether ZOS will commit to doing that... /shrug