I'm pretty sure "Canon" can only truly refer to what we've seen on screen. I think I've read that on these boards once or twice
No, canon is whatever the creators say it is. Some people have this strange idea that it's something imposed
on the creators by some hypothetical outside entity, but it really just means what the creators themselves choose to include, and generally means anything that's generated by the creators themselves and fits into their vision and intentions for the franchise. That's why the
Babylon 5 canon includes the Del Rey novels and DC comics, why the various Joss Whedon shows' canons include some or all of their respective comics, and why Jeri Taylor considered
Mosaic and
Pathways to be canonical while she was working on
Voyager but her successors didn't include them. Conversely, Roddenberry used a restrictive definition of canon that even excluded things that
were onscreen, such as the animated series,
Star Trek V, and selected aspects of TOS (such as the smooth Klingon foreheads). Defining Trek canon is a bit trickier than with other franchises because there isn't a single creator in charge of everything, so the definition has not remained constant over time.
So the reason
Star Trek canon has traditionally excluded offscreen tie-in works is because that's the policy the creators chose to follow -- and more to the point, because the creators of the shows were not in a position to directly guide or supervise the tie-ins and so they didn't represent the creators' vision. But as we saw with Taylor's novels, the current creators of onscreen Trek
could choose to count offscreen tie-ins that they directly supervise or generate as canonical, if they so chose. The Abramsverse tie-ins are closely enough supervised by Orci/Bad Robot that they
could be treated as "expanded universe canon" if Bad Robot and Kurtzman/Orci chose to do so.
But I don't think they will. Despite what Orci said when practically browbeaten into it by the interviewer, he previously said that he "arrived in Star Trek where the rules of what is canon had already been established." And he's said that on many occasions before. I don't think one interview is going to change his mind.