It's inevitable. In any online game, there will be trolls who love to ruin the experience for others, and The Division is no exception. Several reports on the internet speak of a doorway on the first shared area that players can block simply by standing in it.
There's already evidence of this problem, and we believe many more will appear in the future (trolls always find a way).
This didn't happen to us while playing, but in that same area there is a computer that you need to access to complete a quest, and we could hardly get to it because of the cluster of players trying to do the same.
Most online games allow player-characters to cross each other, and in large part this is the reason. We will see what answer Massive has to this problem.