I'm interested in pre-ordering for steam but the option isn't available, I'm wondering if it will be later.

Depends on if it will be available on Steam. Chances are it will be but we don't know for sure yet. If it is you probably just have to wait a few months. But why preorder on Steam anyways? Can't you just buy it the second it appears for sale?

You won't see it on Steam till about September, October maybe. When the game is closer to release.

If it's going to be available on Steam at release they might put it out for pre orders a few months in advance.

Why would you preoder a game on Steam when you can just buy it the second of release anyway? It seems unnecessary and who knows you may change your mind by the time it comes out.