I can see it coming soon in the obituaries:
Some time in 2017 or 2018, at a date that is much in dispute, private and public PaaS died of neglect. While once a part of the NIST definition of cloud computing, PaaS lived a wonderful life in the early days of cloud computing as a place to build new cloud-based applications. Standards were formed around PaaS, and even today upon its death, PaaS is surrounded by many friends and family. PaaS has been survived by public IaaS platform services that offer better and more versatile development tools.
These days, much of what PaaS provides, including quick and easy development tools and quick ops deployment, have been replaced by IaaS providers. Public IaaS clouds, such as Amazon Web Services, now offer features such as container-based development, serverless computing, and machine learning and analytics that have made a feature-rich IaaS platform the best place to build and deploy cloud-based applications.
What also interesting to note is that most major public IaaS cloud providers also provide a PaaS as well.
What’s happed is combination of choice and momentum. Developers, who are these days mostly charged with the migration of application workloads to the public IaaS clouds, have to avoid PaaS. This is because PaaS clouds typically require adherence to specific programming models, languages, databases, and platforms. Thus, while PaaS is good for new cloud-based applications, you can't easily fit some traditional LAMP-based applications into a PaaS platform. To do so means major rewriting, cost, and risk. So, bye-bye, PaaS.
The initial PaaS momentum was around the explosion of platform services that are now a large part of IaaS clouds. These services, along with platform analogs for migrated applications, are now all on the same IaaS platforms. What is more, these platforms provide state-of-the-art cloud security, as well as operational services such as management, monitoring, and business continuity and disaster recovery. In short, today's IaaS platforms provide the Pass features that PaaS platforms provide plus the PaaS features that PaaS providers never provided.
Of course, technology never actually dies; it morphs into other technology, and I suspect the same will happened with PaaS. All the big IaaS providers still maintain a PaaS; indeed, some were built upon an initial PaaS offering and quickly pivoted to IaaS cloud services to keep up with the market.
However, the concept of PaaS is really what has died. The notion that a public cloud service was a platform for the building and deployment of cloud-based applications, and thus would be the preferred way of doing so, just has not survived public IaaS platforms.
Who would have thought that IaaS platforms would become more than just storage and compute services? Not the PaaS providers. But that's exactly what has happened.