The Council is not in charge of CSSU. It is a community project, but it's up to their maintainers to decide what to include in CSSU. So to include any system package in CSSU, you must first ask MohammadAG and/or merlin1991 if they are willing to include it.
Best way to include anything in CSSU seems to be through IRC communication with actual maintainers (expect some resistance, however).
The only question that The Council is able to deal with, is about the possibility to add dependencies with CSSU packages in Extras applications. That has been proposed previously, and seems quite reasonable, as it will allow app developers to use updates libraries such as Qt and others. Unfortunately, up to now we haven't had too much control over autobuilder and repositories and every time we had tried to fix any issue, it took ages. This is something that should be improved with the movement to self sustained infrastructure and with the new community OBS, however, do not expect it to happen very soon. My personal view on this thing is that if you join the CSSU team, more underliying libraries and core components could be upgraded in a cleaner way. Definitively, upgrading this stuff via Extras is not a sane path.