I'm able to read the value of the plugin defined cvar after moving the map option from the configuration file to the start cmd, thanks to Lev2001 on the bug tracker.
I'm unable to read the value in plugin_init/plugin_cfg, and able to do so only after the first round has started on the server. I was under the impression that the value would have been loaded prior to plugin_init as I don't find anything on the docs that would indicate otherwise.
Is this expected behaviour? Or should I have been able to read it in plugin_init?