This may have been a conscious decision, but the plugins that we use to install widgets, sql etc are not usually the ones that are used for functionality. We usually have a Core plugin that manages the functionality outside of installation. So we have something like this.
CorePlugin - Plugin Group
SQLScriptInstallerPlugin - Child Plugin Does SQL installation and stores connection string
However, it seems if we call "PluginManager.Get<SQLScriptInstallerPlugin >()" as we now need to get the connection string and schema from the Initialize of CorePlugin it returns null?