When we started the West Block project, there was an assessment of whether the MacKenzie Tower could be turned into occupiable space. There was no feasible way to meet the modern building code in the MacKenzie Tower. Although the Prime Minister's office is at the base and there's a family room space above that, there's really no functional space within the full height of the tower proper.
On December 11th, 2018. See this statement in context.