This has not been planned so far. By the way deltarpm is now available as a package in devel repository and I’ll need to evaluate the compatibility with openmamba updates management infrastructure, this will take a long time or maybe not. Meanwhile, thank you for suggesting.
openmamba uses smart as lower level package manager, which doesn’t have deltarpm support (see also https://bugs.launchpad.net/smart/+bug/245428 ) and smart itself is not really supported anymore. So supporting deltarpm implies changing default update manager to e.g. yum. Although changing to a more supported and recent package manager would be convenient, this is a major change which will require a lot of time before being supported, at least for what I can do these times.