Import 2D assets at run time

I know that Unity isn’t really designed to work this way, but I was wondering if for my 2D game anyone had any advice on how feasible it is to import ALL of the 2D textures from the hard drive (pngs & jpgs) at runtime. I want to build atlases dynamically for them so that it is still a small number of draw calls. It would obviously be a bit of work to set up but it is one of the project requirements.

I was probably going to use NGUI or 2DTK for this project so that may simplify things a bit but from what I can tell it might be complex and have some serious performance implications.

Any advice would be appreciated!

This may help you
http://forum.unity3d.com/threads/unity-2d-loading-sprite-atlas-from-web-and-using-it-at-runtime-dynamically.234128/