Hello,
well it would be nice... but as you say, it would be only possible if a Flash or Java would be used for uploading files.
With standard HTML-based upload, this is technologically not possible. You can surely used an animated image or something to "amuse" the user, but you cannot get real transfer data to show a realistic progress bar.
However, using a flash-based uploaded as is already integrated in Joomla media may be implemented in future.