I doodled up some code to thread up some textures (using that mostly broken airlock code discussed 2 posts ago), as a few of the 1600x1200 beefy ones I have take a few seconds.
image_manager.Load("background "); will do the magic, and the texture can be referenced by filename later ala image_manager.Load("full_image "); and the texture should be already loaded. Or not, in which case it goes back to the normal blocking load.
Unfortunately, I fear this will be of dubious practical usage. Good to get multithreading experience though, even if it is "threading that gains minimal practical benefit"...