After PS-235, QRT plugin has two variables to control whether logging is enabled: 1) global-only, dynamic query_response_time_stats; 2) global/session, dynamic query_response_time_session_stats.

For next backwards-incompatible version consider merging the two variables to a single global/session query_response_time_stats.

Also, technically QRT consists of several different plugins under the hood: one audit plugin and several INFORMATION_SCHEMA plugins. The plugin names influence variable names, originally some variables ended up in the "wrong" plugins, requiring brittle synchronization. Thus investigate whether some variables can be moved to their naturally-owning plugins.