The renaming of the MedicationStatement Resource to MedicationUsage, and the related constraining of its scope, will represent a major barrier for implementers wishing to move to R5; particularly if international uptake of the R4 version of the IPS IG reaches the targets set by the GDHP/ONC Project (i.e. 20 countries by the end of 2022). Furthermore, IPS derivations that implement the MedicationStatement resource, are in production use in some countries, e.g. New Zealand.

The reduction in scope is illustrated by a comparison of the Status Codes available in R4 (active | completed | entered-in-error | intended | stopped | on-hold | unknown | not-taken) with those available in R5 (completed | entered-in-error | unknown) - noting that the binding strength to the related Value Set is required.

The fact that the word 'statement' is still used 17 times (reduced from 19 since my last Jira Ticket on this item (31968) on the Resource Profile Page is, of itself, indication that this re-naming is unsatisfactory and, IMO, it's stated purpose is very likely to be confused with MedicationAdministration by implementers. 

Medication lists are used to fulfill a number of different uses cases throughout the world - many transactional (i.e. all prescriptions, dispense events and administrations with regard to a particular patient) and beyond pure usage of the medication.
 
From long practical experience as a Senior Architect in the NZ e-Prescription Service, patient management system developer and contributor to the NZ HISO standard for Medication Lists, it is rare that any community (i.e. non-hospital) EHR software records actual administrations - so the ubiquitous Status Code from the constrained R5 value set is likely to be 'unknown' which is not going to be particularly useful.
 
If those in some countries wish to enforce this constraint, I respectively suggest that it is done via profiling and core/base IGs, rather than attempting to enforce it on the rest of the world.