The hash power that the network currently has it would be impossible for any singular entity to gain control of 51%. Could have happened in the early days, but I don't think this is a viable threat any more.
well not really impossible, it's actually doable, the point is that no one will do it because they could harm themselves more than anything else
You are wrong in assumption that hash power would stay high forever.
unless the price drop too much, i do not see how this will change in the future