The code that checks serverGlobalParams.clusterRole for RouterServer in exclusive mode is:

• analyze_shard_key_role.cpp
  • analyze_shard_key_role.cpp#L43
  • analyze_shard_key_role.cpp#L53
  • analyze_shard_key_role.cpp#L66
  • analyze_shard_key_role.cpp#L79
• query_analysis_sample_tracker.cpp
  • query_analysis_sample_tracker.cpp#L153
  • query_analysis_sample_tracker.cpp#L157
  • query_analysis_sample_tracker.cpp#L174
• query_analysis_sampler.cpp
  • query_analysis_sampler.cpp#L229

We need to investigate that code in order to decide if it is MongoS only or we need to change it to be compatible with the embedded router.