They might have trouble selling their chips. They optimize far more towards performance over price than Qualcomm does. Apple can afford to do that, because of its high profit margins. Potential buyers probably couldn't afford that tradeoff.
So what you're asking is not only for them to sell their IP to 3rd parties (a business model of partners they've repeatedly crushed) but also to build out an entirely separate chip design team focused on a new market.
That’d also be consistent with their past history of trying to pick some edge for a particular market: optimized for media processing, ML, VR/AR, etc. rather than just competing with x86 for the generic workloads. I still don’t see it as a high probability but I’d expect a niche if it happens at all.