I was just wondering, in games I only really make and play as one character (starting over even in diffrent factions has never interested me) so I was wondering, how much of the other factions areas will we be able to explore?

None.

But that could change.

As Valkar said, you won't be able to as far as we know. But a lot of people have been upset about this, so ZOS may change it. You'll probably be able to explore the enemy regions, but you won't be able to get quests there and such.