Dear ZOS, not "not interruptable". It is still a whole one second of doing nothing. Dunno about PVE and healers, in PVP in that one second I will recieve two dawnbreakers, five lethal arrows, eye of the flame, grothdarr proc and surprise attack. PVP is not a place for making choises and deep thinking, the most of time it's "you should already done something". In this case class base defense should be casting immediately.
Please, do reconsider.
And Cyrodiil beyond magsorc problems:
Tested it yesterday and today.
First, had two loadscreens about 2 secs each while just riding not far from Bruma. No one else was around, ping ok. My hardware and connection are ok too. What do you think will happen when there will be fighting zergs?
2nd. Carmala outpost has a too perfect offensive siege spot on the bridge infront of it. The bridge is also going to be the best bow-gunking spot in Cyrodiil ever.
But Winter's Peek looks impossible to siege. No serious efforts needed to just fire everything from above to kill anything moving around.
Except for same "disadvantages" for the attackers/defenders, you should very carefully add such "interesting" areas when the game still has instant loadscreens in the middle of empty nowhere. Have pity on your own servers.