The enableMajorityReadConcern:false option exists on 3.6, to allow the server to avoid holding on to all history since the majority commit point. We would like to add this option on 4.0 to address pain due to commit point lag in replica sets with arbiters.
This work should include adding the enableMajorityReadConcern:false Evergreen variant to 4.0, which was introduced in
SERVER-36083. This variant should include all of transactions tests on 4.0.