I am not aware of any substantial implementations using the SNOMED CT observable content. Pathology has been dominated by LOINC. Other areas of healthcare may have adopted SNOMED CT observables, but we have limited transparency of this and usage. I'd expect whatever decision would be handled as general change management.
As for impacts. The "disruptive approach" of creating new concepts is the safest as implementers and message recipients can easily identify a change has occurred. Though I appreciate a pragmatic approach may be desirable, if taken we would most like generate a list of affected concepts and request all implementations check for the usage of these concepts.