I don't have a source, but the last official rumbling I heard was to add a south-side platform to lower station. This would move the staircases further south on the upper station and distribute passengers better. It would mirror what they've been doing with the passenger management barriers and helper staff.
The ideal would be to add platforms/tracks to the upper station, but this is technically difficult due to where the support columns for the HBC skyscraper are. I would expect adding platforms/tracks to the upper station to cost a lot more than $340m.
Makes sense. Basically repeat what they're doing at Union on the Bloor-Danforth tracks at Bloor-Yonge. I used to take that transfer every day, and the Bloor line platform is dangerously narrow for the number of people that it carries.
Of course, I still think that this should happen AFTER the DRL is open. $340 million is 1km of the DRL. Not a huge amount, but not insignificant either.