The last official report to the GMC was in may 2017 when they said:
Future Milestones Planned
Substantial Completion of Stage 2/3 currently expected in February 2018 (excluding York and Bay Street moat covers; mid 2018), which includes the restoration of the Bay Concourse, VIA Concourse, Great Hall, remaining retail areas and East Wing exterior façade. This will trigger the turnover of the Bay Concourse to Metrolinx for final fixturing. After this time, the City will have no control of the actual timing of the opening of the Bay Concourse to the public.
Updated Schedule
Project completion is currently scheduled in early 2018. This is based upon and within the parameters of the awarded Stage 2/3 construction contract to Bondfield Construction Co. and represent their contractual schedule. Note this completion date excludes the Bay and York Street Moat Covers per the construction contract. This remains a very challenging objective and the project team is working diligently to achieve this target.
See:
http://www.toronto.ca/legdocs/mmis/2017/gm/bgrd/backgroundfile-103901.pdf
It should be noted that 'project completion' means that the area is ready to be turned over to GO so the Bay Concourse may be 'finished' in late February (?) but will then need LOTS of work by GO.