As I understand the leaked plot summary, the Romulans travel back and disrupt the time line, hence the story focuses on a young Kirk, Spock and company. Canon will be followed, but the time line disruption will also allow for some changes to canon to ripple forward, thus “reviving’ the franchise, whatever that means.

Nimoy will cameo as old/’present day’ Spock, who will somehow advise his younger self (Quinto) who will in turn thwart the Romulans. Kirk is dead ‘at present’. Shatner can not play his younger self, (duh!) so absent a worthless cameo as a nobody who was kicked out of Starfleet Academy for cheating decades ago, what role is there for Shatner?

Abrams has a singular opportunity to reset and restart the franchise. If this reset is successful then more movie (perhaps a return to TV), etc., if it fails then Trek is likely dead for decade or so.

Either way, Shatner is part of what was, not part of what is.

It was either he’s in the movie and it focuses on him significantly, or he’s not in the movie at all.