Back in the good old days of Ultima Online I loved the fact that my guild had the ability to declare war on other guilds. Will this be an option in ESO do you think? Will you be able to declare war on other player guilds and be able to fight them if you see them/

Also, I saw someone post that you will not be able to see people of other factions unless u are in Cyrodiil; is this the case? Could I Not be PVEing in other parts of the continent and see members of opposing factions running around but just not having the option of attacking them?

Possibly, not much detail has gone into guilds yet, but I wouldn't doubt it. As for the not seeing anybody from other factions, you will be able to, Cyrodiil is just the only place where you will be able to combat them.

You won't be able to fight your own faction, and the only time you will see other factions is while you are in Cyrodiil to PvP. So there is no need to declare war on guilds, when the only guilds you can kill, you are already warring against.