(Ustr, micro string API)
(and-httpd - simple, fast and secure)
(String library comparison)
Well yum is almost certainly the best for constrained metadata download bandwidth, due to the fact it will (by default) only download the file or changelog data when yum needs it to do some operation (most of the other options want to download everything at once). So in the simple case of installing a single package, it's very likely that you can just download the "primary" metadata file.
But, yeh, even so that can still be relatively large if you want to install a small package over a modem. yum-presto will be available/integrated in Fedora 10, which I think is a step in the direction that'll help (it provides/uses delta information).
I don't think we want to standardise anything right now, because I don't think anyone knows what the final solution is going to look like (repo. metadata was only standardised after a few different people had tried different things, and the problem was fairly well understood -- and it's still far from "perfect"). But saying that, we do keep in touch with the SuSE/zypp developers.