The goal here is to move towards removing the internal view catalog logic where we support having invalid views. Regular user writes to <db>.system.views collections is supposed to no longer be allowed re SERVER-43633. However, applyOps appears to be a loophole.

I believe the idea is that downstream teams want to take oplog entries and directly apply them to mongod servers via applyOps. So perhaps there's a way we can add validation logic here, where primaries at least can error – some investigation of how downstream teams use applyOps is necessary, to determine what we must support versus can prevent. Update: Max thinks mongomirror might not use applyOps for views after all.