Pretty simple suggestion. This is one of my least favorite things about sharing via Dropbox; pretty much every conventional image host has rather short links, unlike Dropbox, where you have to jump through some hoops to get the shortened version.
I will need to check how and where we change this, not from a technical perspective but in the GUI. Currently we are redesigning Greenshot, so let's see where this fits as soon as we are finished with the biggest parts.
Just stumbled across this, it seems that this problem has been solved by Dropbox in the meantime. By default, they return a short URL if not requested otherwise: https://www.dropbox.com/developers/core/docs#shares