The random order adds to the speed, if you take that away, the file download will be slower, or at least will need more seeders. Why would you use torrent in that case anyway, a simple mirroring system would be enough. Mirrorlists allow for updating the list of "currently online hosts", linux package repos use this setup, and it's very reliable.

As for random seek (what you describe at the end), you need an index. AFAIK, an index can't really work without the complete file.

Technology enables a lot of things, but it's not magic, can't really make things happen that are physically impossible.