People who didn't think Shepard was going to die didn't pay close enough attention to any of the three games. First off, he is plastered with more religious savior symbolism than my Hispanic ex-girlfriend's uncles low-rider, he "died" only to triumphantly defy fate at the end of ME1, he literally died and was resurrected via a project entitled Lazarus, his name is Shepard for Christssakes, I could go on and on.
If surviving situations that initially seemed to kill him makes you a Messiah, then Arnold Schwarzeneggar and Bruce Willis play Messianic roles in the movies on a regular basis.
The Lazarus Project was just a stupid way to negate Shepard's choices and advance the timeline.
Commander Shepard was named after Alan Shepard. Who (not) coincidentally, was the first commander to use red stripes on the arms and legs as personal identification during the Apollo 14 mission.
So no, Shepard's "sacrifice", and I use the term very loosely, was not foreshadowed AT ALL. I find it extremely easy to believe those rumors that it was cooked up by Walters and Hudson in some misguided attempt to be "dark and edgy" because shows like Game of Thrones and Breaking Bad are so popular nowadays.
Besides which I don't give a sh*t about playing Shepard again. I was ready fro that story to end with ME3 even before that game was released. My beef with that is Shepard's story ended so badly, yet Bioware is not in the least bit contrite about that, essentially blaming ME for being too stupid to appreciate the Art behind it.
What I do care about in this case is the essentially slash-and-burn attitude towards the Mass Effect setting. Go in, trash an entire freaking galaxy, rendering it unusable, and moving on to a new one, pretending the screwup never happened.