Spock To Appear In Star Trek Discovery, Red Letter Media Hardest Hit
There are no 21st century Star Trek experts more knowledgeable than Mike Stoklasa and Rich Evans of Red Letter Media*. Witness the cynicism and melancholy that only loving fans who've been seen the long, sad decline of the Star Trek franchise can bring.
Coming from that perspective, you might be able to see how bringing Spock back is fan service intended to drive viewers to Star Trek Discovery.
On the other hand, it could be a deliberate attempt to bring Discovery more into the traditional Star Trek mold.
* I highly recommend RLM for some of the most insightful, wry and hilarious movie reviews. This doesn't necessarily apply to fans of comic book movie universes.