I would like to set sub-item default values like I can with regular items. This would help set the default status.
I am very interested in this as well, would be so helpful.
Hey @samjtaylor
We developed an app called subitem automations that provides robust automation capabilities to subitems. It also allows to set subitem default values, here are two examples →
There are many more options 
You can find it in the monday.com marketplace in the platform or here - monday.com: Apps Marketplace
Hope that helps!