We don't want a gallery from threads, but the existing gallery popup window to display all of the users images in their gallery and attachments to allow them to click on an image to insert it into their post (inline).
Could you create a thread on the request forum (sonnb.com) about the detail? There are some ideas around this thread. For the original idea I do not think it will be available. Thread attachments are separated from the XenGallery. If you wish to see them in XenGallery, you can import at anytime.