You're all making this much too complicated. Who needs the client to make multiple requests when you control the server? Client does "GET /" and the server starts sending a large index.html using irregular sized packets at specific intervals.

But suppose we broke it, now we have to fix it, right? Start padding everything to power-of-two size boundaries with a minimum of 16. Or if that would make Tor traffic too identifiable, then instead add random()%packetsize padding to each packet. Either would reduce the number of detectable packet sizes below a 1500 byte MTU to 8 at the cost of less than doubling the bandwidth consumption.

I think this will be a bit harder, as you don't really have control in what order the images are being loaded. They could be loaded in parallel for example. If you try to circumvent it by adding delay's on the server side you quickly block the browser as you will reach the maximum amount of parallel connections.