No idea how pricing might work for images/articles.
Most magazines buy one time first serial rights. So the issue runs and then a month or quarter later its off the shelf and the images/articles only rarely get a reprint. As an originator you are then free to try and resell the same image/article (albeit very hard). So your right in that shelf lives might be indefinate.
Maybe it moves to some type of royalty based on the number of DLs…
With regards to comp I would think it would be structured much like it is today where its dependant on sizing from postage stamp, insert 1/4, 1/2 full TOC, dd truck/cover…no way to know for sure.
What would/will give me cause for concern is potential for copyright infringment. Where today all our 1024 x750s or 800 x 500s images in gallleries are totally unuseable for print where they want to be able to print at a minimum of 8.5 x 11 300dpi.. Someone could rip images and submit them as their own. Publishers wont need full res files anymore.