CMS 159 requires use of stratification. QMIG STU 3 locked stratification down to a single population to provide ability for designating what a stratification should apply to. But the update was overly aggressive, since only one population could be designated at a time. Refer to https://hl7.org/fhir/us/cqfmeasures/STU3/StructureDefinition-computable-measure-cqfm.html. In QMIG STU 4, this functionality has been updated so that the applies-to extension is not required, if all populations should be stratified within a group, or a subset of populations can be provided, if a stratifier should only be applied to a subset of populations within the group. 

CMS 159 requires 2 stratifiers to be applied to all populations within the group. There are four populations in the measure - IP, Denominator, Denominator Exclusions and Numerator. To achieve this currently, eight stratifiers would need to be created - one for each of the actual stratifiers times the number of populations. Though it is possible to add this number of stratifiers, this functionality is not equivalent to QDM behavior, and it will cause a lot of confusion.