Realistically, what is planned right now, or available for use with minimal investment is this

Green is the platforms at the tower centre - Calgary's train station. There is no reason to believe we will build a new more expensive station when we have one already especially when service is so limited to begin with.
The boxes are station boxes for LRT subway (with the stations moved maybe a bit from the current drawings, but those will likely change whenever the subway report comes back).
So what does that leave us for building connectivity and additional facilities?
Station head for the 'hub' in either the ATB branch (which would be repurposed or rebuilt depending of heritage value), or in the Scotia Bank banking hall. Concourse level connecting to the 'theatre' level at Bankers Hall, and into the Unicorn pub in Home/Dome connecting up into the food court on the inner part of the Lorraine building.
As for tower centre, it is pretty easy. underground concourse from the 10th Ave LRT station under the heavy rail platforms across into the convention centre concourse.
It isn't perfect but it gives two protected from weather transfer stations that would both easily connect up with a future 6th Ave subway. It would be pretty bold in and of itself while not being too flashy.

Yellow is connecting concourse, which would reuse what already exists as much as possible. Solid blue and pink are the options for a station head. For those wanting a 'grand' station, the base of the tower centre I am sure could be opened up and expanded into a very grand waiting hall for far less with much better results than something new.