I have a business user who needs to download a special jpg rendition from a PSD (in bulk ~ 100 at a time). We currently create the rendition, but the only way to download is to select them, click download and remove the "asset" option and select the rendition. This works, but looking for a way to help make this easier and thinking Desktop or Asset Link might be a solution.
It's a great request, but not currently supported by either feature. (For that matter, I'd love the ability to link specific dynamic renditions or smart crops in InDesign documents as well).
Both Desktop App and Asset Link are not designed to extensible, so the best way to accomplish this would be a custom panel in Photoshop (or perhaps Bridge) that accessed the DAM and pulled the relevant rendition.
We recently built an application to relink InDesign documents that were created locally to images and graphics on AEM Assets in bulk. It'd be a similar type of custom panel and it sounds as if you'd need to do some sort of search against the DAM. Bridge would be more natural in some ways, but I know we found that piggy-backing on the Asset Link functionality was a LOT easier in InDesign than for functionality rather than rebuilding the connection from the ground up, so Photoshop may make more sense.
For that matter, if you don't need a lot of flexibility / user interface elements in this request, it might be easier to create a small script that executes a curl command over a defined set of assets and pulls down the relevant renditions. The curl itself to pull the rendition would be pretty easy--the harder part would be the query logic to point the command at the right assets. Maybe you could have users create a collection and point the script at the collection? In any case, this would be a less nice UI, but a lot easier to build than a panel solution.