First of all, my concern about security problems was first and foremost related to the resource question. I think the shipping issue is more of an economic issue, where you actually will have new commercial infrastructure related to the sea routes.
Of course, if you have important sea routes through narrow straits, as historically seen, that will often create some kind of tension, because the narrow straits will suddenly become strategic important choke points. In that respect, you could argue that a rerouting of the shipping lines, if you see it all the way through, will create new choke points and thereby will also create a new security dynamic. It does not necessarily have to be negative.
I don't know if it's too easy to say that the world has a constant security potential, and if you remove one hot spot a new one will emerge somewhere, but that is definitely a very simple way of looking at it. If the Suez Canal and the Panama Canal, for example, are losing their importance because the majority of the shipping will go another way, that potential may move to another area.