IIRC the design and planning for the connection between Exhibition Loop and Dufferin Gate Loop seems to be even farther along than the planning for the Union and Queen's Quay expansion and the extension along Queen's Quay East. Granted, the Exhibition Place extension is a far simpler and less expensive project, but I think it's pretty likely that we see the connection to Dufferin open well before the Union & Queen's Quay expansion and the QQE extension.
This file was probably posted in this thread a long time ago, but this shows the striking level of design already on the Exhibition Place extension. I haven't seen anything near this level of detail for the Union/QQ expansion or the QQE extension, but please feel free to correct me if I'm wrong and if there is more detailed design done on either of the two extensions.