jscore tests can run configureFailpoint. In case of a sharded fixture, the failpoint will be enabled on a mongos.
Currently the behaviour is disabled for cluster with multiple mongos because that would cause only one mongos to have the failpoint configured. Subsequent commands (including the disabling or waiting of the failpoint) could still be randomly dispatched.
However we could solve this easily by

• pinning the mongos used to execute configureFailPoint with mode "alwaysOn" (if the command returns "ok")
• redirect any subsequent command against the pinned mongos
• unpin once we received a configureFailPoint with mode "off" (if the command returns "ok")

We should also manage the case of nested failpoints, and unpin only when received the last configureFailPoint with mode "off" 
After that, we can enable multi-routing on the excluded tests which can be found by looking for

// pinToSingleMongos due to configureFailPoint 

TestData.pinToSingleMongos = true;