At some point we decided the announcements would be staggered since the process is not synchronized.
There's no harm in letting CmdStan (and MatlabStan, StataStan, Stan.jl, MathematicaStan) users know that the interface they use has been updated.
@bgoodri waits for the CRAN mirrors to catch up before announcing. I think that's reasonable. There's still usually a delay between a CmdStan release and RStan, so just announcing when ready seems like the right thing to do.