Hi Rangeen,
I was thinking about your idea about implementing multi part download for yum. I am sorry but i dont see why it would be useful. First of all, if you are downloading same package multipart, it would have improved the rate of download, if we were downloading the package from different sites simultaneously, which is not the case in yum. Also secondly, if you are planning to implement this when more than one package is being downloaded, i again dont see whether it will be really useful. For example, if you are downloading a group of packages and one among them fails dependency check, then all the packages downloaded after it also wont be useful. so there is no point in downloading them out of order.
Please correct me if i am wrong. I havent used yum myself, i just assumed that it works similar to yast where in packages are installed as soon as they are downloaded and in the same order as they are downloaded.