All underground stations were built for them. Renovations might have changed it a little, however, in some of them.
Looking at the layout, wouldn't be hard to install them in all of the DT stations, Coliseum, Southgate and Century Park.
Churchill, Central had them, Bay, and Corona were built for them. Government Centre and University were not. In particular there is one elevator at University that goes from street level to platform level which sort of falls outside of the traditional fare collection areas. I think Government Centre is fine. I know for sure the south end you need to transfer elevators so the elevator to platform level can fall within the paid area, but I am not 100% sure about the north end. Central and Churchill's elevators fell outside of the fare paid area for the turnstiles. They had separate machines for fare collection that didn't have the turnstile component. Essentially back when the LRT opened, you could avoid the turnstiles just by using an elevator Downtown.
Central's elevator could easily be incorporated into a new fare paid area controlled by faregates, Churchill's would be a bit harder. Bay and Corona were designed a bit better to include the elevator in the fare paid area, but, Edmonton Transit had
I do think fare gates are a way to help. My first experience goes back to 2005, when after a trip to Toronto, I found it remarkable how little security I saw in the stations, but, how safe it felt. And I mean I generally felt safe in Edmonton already, but, the TTC's subways seemed just that much safer.
This $400 million figure out of Calgary I think is crap. I think this is a consultant who has gone to the extreme to dissuade Calgary from even considering faregates for whatever reason. For $400 million, that figure must include significant modifications to 7th Ave stations to create faregate controlled areas, and this would mean building a lot of walls and/ or fences.
Vancouver was south of $200 million ($186 million?) for their entire Skytrain system. I saw something from Tim Cartmell about a unsolicited quote of $30 million to do Edmonton's LRT system.
The two new NLRT station don't look like they will support faregates too easily.