Nike posted pictures of both Shalane and Kamworor today on Instagram, along with an ad for the Zoom Vaporfly 4%. Noticeably, neither of the pictures are from the race. The pictures out there of Shalane breaking the tape don't have any visible NB logos in them, but I guess it's still reasonable to assume that pictures of the NYC finish line amount to promoting a competitor's event.
I think the contract questions raise the likelihood that she'll retire. If she wasn't talking about retirement, I agree with previous posters that I could see her going to Skechers or even Hoka or something for the final act of her career. But that would be a big gamble as it would also mean a new coach and leaving the group she helped create. That sounds pretty daunting and ambitious, and she hasn't said anything to suggest she's up for that.