If a plugin cannot be loaded, there is no information about it anywhere. Even if the plugin is a mission-critical security-related one. IMHO, there must be a way to configure a plugin as a "must work one" and the engine must raise error if such plugin failed to load.
I like an idea of adding configuration info to distinguish required and not-required plugins. But may be better mark plugins that may be not loaded? Currently I know only one in default configuration - engine12 in client case. When adding non-default entries mentioning in them not-required plugins will be possible but hardly needed.