Call me overly optimistic, but I'd like to think that after the giant clusterfuck and backlash over what was done with Mass Effect 3, BioWare is actually going to try a lot harder to respect the choices made in previous games and have those choices matter and actually shape the narrative and not just get abandoned in the third act of the game. People keep using the Leliana thing but, well, that was actually kind of/sort of explained.
In 'Asunder', as well as Dragon Age 2 (and, rumor has it, Inquisition), it's hinted that if you killed Leliana you *killed* Leliana; e.g. that shit happened. However she is restored to life by some unknown means. Magical, Divine, that's not clear. In point of fact if you killed her she may not be 100% Leliana anymore. Think Starbuck after she "died" in Battlestar Galactica.
Gaider decided that she was important to the narrative so she makes a return; that doesn't mean the choice to kill Leliana wasn't respected per say. Also I found that *all* my choices from Origins were reflected well in Dragon Age 2. I'm sorry that some people just can't get around something as banal as "I want that character to stay dead!" even if said character being alive is rationalized to even a minor extent.
Anyway, as to how they'll do it? Well, if it's going to work across all platforms there's really only two ways I can see them doing it for consoles; basically you'll have the option to save to the cloud (which both PS3 and 360 have access to at present) and both the Xbox One and PS4 will be able to scan your save files there, or you'll be given the ability to chose major plot events as you *somewhat* were able to with Dragon Age 2 where you could chose if the Warden survived, etc.