I just sent this feature request to the whatwg mailing list, and I thought I would toss it this way as well. Basically, the pain point is that extra http requests are a real performance hit and large web apps tend to have to do a lot of work to get down to the fewest requests as possible. The suggestion is that there be a way to load a zip or tar file that can be used as way of priming the cache (or other storage mechanism) so that other resource requests do not require a trip to the server. For example, instead of creating css sprites, all images could go into the zip file, and still be loaded in one trip, then when the css required it, it would be pulled from the cache instead of requiring the trip to the server.

This seemed like something that could also tie in nicely to the local server mechanism.

Here's a link to the whatwg mailing list post: http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2008-July/015411.html.