The WMS capabilities document currently exposes the list of all the geoserver supported CRS's.
This issue though, is not meant to actually limit the list of CRS's geoserver can operate with, but to just limit the list of exposed ones. So if a request is made over a supported CRS that is not listed in the capabilities document, it should keep working anyways.
Also, a very basic user interface configuration element shall be included, so its not that hard for users to specify the list of CRS's. This may be as simple as a text area in which to write a comma separated list of epsg codes to expose.