How to use sprite sheets effectively and responsively in Craft
I thought I'd just add my two cents, since no one has answered this yet. :)

It's not clear from your question if these image elements are purely front-end design assets, or if the client/end-user needs to update them from within Craft. 

In the case of front-end assets, my opinion is that how these are used in your site is part of the projects build phase, and not something Craft should be responsible for. If Craft starts implementing support for generating sprite sheets, there're tons of other front-end stuff that would be just as relevant to add. Compiling SCSS/LESS/Stylus, concatenation and minification of CSS and JS, building web fonts from SVG files, minification of images and SVGs, etc. I don't feel that this is what P&amp;T should spend their valuable time on. :)

There are numerous ways to automate building a sprite sheet as part of the build, I use grunt-spritesmith which also gives me a complete stylesheet with classes for all the different elements.

If the problem is that the client needs to update the assets, I see why the sprite sheet has to be generated by Craft. It would be possible to make a plugin that creates a stylesheet from all images in a folder, a list of images or something like that. It would probably involve a lot of inline css, since you wouldn't know the sizes and positions of the different elements in advance. 

But, depending on the nature of the elements I'm not sure if I think it's worth it.  Since you're considering making a sprite sheet I guess that the elements isn't actual content (ie images that should be accessible, searchable by Google, etc)? In that case I think I'd just lazyload them if they result in too many requests. If the elements is actual content, combining them into a single image would really ruin accessibility, so that is a really bad idea anyhow.