This seems out of scope for the RFC process as it describes problems that are:

• already solved,
• or; solvable with minor changes to the DismissableSiteNotice extension that do not affect the overall architecture of the extension (out of scope for TechCom to proactively lead decisions about).
• or; solvable with changes to CentralNotice that don't affect its overall architecture per se. (If and when such proposal is accepted by the maintainers of CentralNotice and the preferred solution requires major changes that are cross-cutting and/or hard to undo, then an RFC could be created for that now, or later).