How are KPIs changing now that CEOs expect more accountability and measurable impact from product teams?

I would start by separating out measuring product health from goal setting. First, every PM needs to have a clear understanding of the key metrics for their product area. This is a baseline set of KPIs so a PM knows how their product is currently performing and which specific KPIs are under or over performing. A good place to start when building a baseline is to use a general lifecycle model and define metrics for each category: discovery, acquisition, activation, engagement, retention, revenue (if applicable). Now not every product has every category, but this will get you a good place to start. 

Once you have a baseline set of the overall key performance indicators you want to monitor day-to-day, you can get a more holistic view of how your product is performing. From there, you can decide on which KPIs you would like to set goals around. Whether you use an OKR framework or some other framework, you should make sure the goals that you set are not only aligned with where you can make improvements in the product life cycle, but also what the CEO and company is looking to drive. 

Once you create this visibility into current performance - it becomes much easier to align the CEO to the goals you would like to set - and in turn it also gives the CEO visibility into how you are going to measure impact and a way to for the team to have accountability to move a specific set of metrics vs. accountability to move all of them at once.