Are non-commercial applications going to be published in the Software Center even if a new version of Ubuntu isn't out yet?
As an answer, may I direct you to this link?
Note the number
I am not sure what you mean by
It is my understanding that
a) Each version of Ubuntu has its own repositories of applications.
b) Canonical will not place software in the repositories (Ubuntu software Centre) if that application does not work well with the version of Ubuntu being serviced by a particular repository.
In other words, if a program/application does not work well with the latest version or it does not meet the design standards that are set for Ubuntu applications, then the application will not be put in the Software Centre for the latest version.