Hi this is a really easy to implement request. Unfortunately I am not cool enough to implement it myself!
When making a post and choosing to add an image, you can currently link the image you've chosen. You can add an image link to the file itself, or the the image page. You cannot however, dictate the target. AKA you cannot choose whether the image link goes in a new window, the same window, etc.
Could you all add this feature? =)