AFAIK devs are expected to be On Call, refine code to handle edge cases properly, make technical tradeoffs (performance, efficiency, ...), grow other devs etc. I assume most PMs would rather avoid those tasks, otherwise they would have opted to be devs in the first place.

On the other hand, PMs spend time talking to customers, studying competition, are involved in GTM and pricing decisions, make roadmap tradeoffs, coordinate across broader initiatives, and so on. Any time spent on technical endeavours comes at the expense of those activities.

Although AI allows disciplines to expand their reach into other domains and conduct their work more independently (shorter feedback cycles), I will be very surprised if it will wipe the value of each discipline's domain expertise, depth and focus.