Personally i would like to see some variety. So many of such backgrounds are of nature or landscapes or clouds. But how about some urban environments, city blocks, markets, shopping malls, streets, office cubicles, a backlot/backyard and so on. Or old/abandoned buildings like an old warehouse or some old shed somewhere. Maybe an old/new parking lot or junkyard. Without people would be a plus but it's not very hard to paint people out if the resolution and pic quality is high enough.

I have done a bunch of projects requiring such backs and always had to go shoot them myself cause there were so few choices available. Yes i know its all boring stuff but it's exactly the kind of images you often need to place behind characters.

Of course if you'v already shot the photos then it's not possible, but perhaps something to keep in mind for your next batch ?