I finally got the chance to play the Citadel Dlc and had an absolute blast. So funny, so much fan service, so many great things to do after the mission.
I hadn't thought about making a personal canon due to the dlc until I read through this thread. I love the idea, I think doing that might actually make the endings playable for me. Doing the mission before Cronos, but the party after the legend save. Maybe it took a long time to fix the citadel, but it may have taken a long time to get the Normandy flying again, to find Shepard too. The keepers may have survived and fixed things even faster than the last time and if you reject the idea of all synthetic life being destroyed, the Geth may have been intact and would probably be very quick and effective at fixing the mass relays and the citadel.
I wonder if they meant for people to do this, probably not, but given the mess that was made of the endings, I very much like this idea. It gives the game and the trilogy a sense of completeness.
It's not a new thing for me, choosing a different spot for the ending of a Mass Effect game. In ME2, I made the end point for myself when you invite Liara to the Normandy for a drink. If I've romanced her, we reconnect, if not, we talk of what's to come. Either way after that, I take the Normandy into Earth orbit, save, then import to Mass Effect 3.