I work at Y+E Centre.
Interior work has been ongoing for a couple of months now. Mostly ceiling work (replacing the disorienting polished SS with drywall).
The afore mentioned Bowring is now a PCL construction office.
In our building (20 Eg W) they have been doing a lot of prep work for at least 6 months, including upgrading electrical systems and plumbing, installing new generators etc.
Just last week as the hoarding was commencing outside, the glass and steel canopies over the entrances to 20 Eglinton were removed, as were the pigeon screens by the Pickle Barrel. I can't tell yet if the removal of the canopies is to commence construction on the retail cube connections, or if it's to accommodate the hoarding for staging for the tower extensions.
That said, we had been told last year that the tower work was at least 3 years away, so I do think what we're seeing now is the beginning of the cube.