Hi,
I'm also waiting for this feature. And it's going to be great not just for the crop tool but everywhere when there is an extra select. Having a user to decide what is their default choice can improve usability drastically. There are currently three tools I change all the time from the default one:
The crop I change to original ratio
The healing tool I change to Current layer and Below
The gradient when on the mask I change to black from grey
I need to do these three actions on pretty much every image I open. You can imagine how much extra movements it creates to change it every time...
Besides this UX issue your app is so amazing, I am really enjoying it!