I made this comment in another thread, but I think it should be its own topic...
With coming update (One Tamriel) players from all alliances will receive more freedom in PvE. But limitation in PvP will be more visible.
What about to add option to choose alliance in entering campaign?
I'm going to go in the other direction on this.
With any starting character able to go to any of the other alliances and play as one of them from the very start, the lines between alliances need to be made stronger and deeper in cyrodiil/pvp areas or the entire alliance war will no longer mean anything.
So I propose that alliance allegiance be made account-wide.
Example: A person may have any mixture of characters that began as AD / DC / EP and played through those first levels from any mixture of Kenarthi / Stros / Bleakrock. When they enter their first campaign, they choose an alliance, and that choice holds for all their characters.
This isn't as strict as it may at first seem.
Consider...Outside of pvp, everyone will be mixed into the same world. Yes yes yes, different instances, but there won't be an alliance boundary separating an AD character standing in wayrest from a DC character standing there. If someone wants to play a EP khajiit, they roll one up and first thing they do is travel from kenarthi to bleakrock and start doing quests/grinding there.
I'm on console, so the text across alliance boundaries will be new, but maybe the fact that there have been so many alliance boundaries that are coming down puts us console people in a position to more clearly see the need for stronger pvp alliance borders.
With effectively nothing to distinguish one alliance from another in pve areas, the capability to have a traitor-alt on another alliance just to do sabotage in pvp will increase. Not to mention alliance point farming, boosting, tel var farming, and eavesdropping. It's a crappy thing to be trying to defend a keep and an alliance "ally" takes your siege when you try to do a quick repair, and turns it around to shoot at your own keep. Or to go stealth to avoid a group of enemies and an "ally" spams light bow attacks at your location, telling those other alliance players you are there.
So, I think the alliance gameplay will need to have cross-alliance players choose. Or the dirty dealing will get worse.