Perhaps not exactly as displayed, but a practical design actually wouldn't look too far off from the concept if you're clever with the stylesheet. Such minor things like the slanted corners and inlets of the boxes would need to go, as well as some other awkward shapes and maybe a few of the gradients. There's also a lot of opportunity for repeating patterns, especially when used in conjunction with the multiple-backgrounds capability in CSS. Glows can be handled easily via text-shadow/box-shadow.
If the concept is optimized like how I explained above, I'd say you could probably get all UI-related assets under a meg total. Hexagons might take up a lot of space though as a .png image.