It would be really helpful to have drafting tools for starting threads. The general idea is that you could type out an OP and then save it for later revision and posting somewhere in your User CP. Useful mechanics within this idea would include post previewing (letting the user see what the final product will look like before posting) and restore points (allowing for multiple versions of the post to be easily compared and selected from).
Right now, if I want to draft something like a respect thread or other post type that requires a longer development, I have to lay everything out and save it with a text editor or my private sub on Reddit. Which isn't the worst, but it would be cool if I could do what I need to here, since this is where it's going to end up anyway and that would make things simpler and easier.
This would also generally be beneficial for the article/blogpost selling point. It's pretty common to have drafting features on other platforms. If GT is going to be any kind of competitive on that front, it seems like an obvious addition.