I don't think that IaaS will absorb PaaS. Ever. They both solve cater to different needs. Especially as application developer, you do not care about stuff, like the operating system. You only need your application environment (PaaS). If you write a Node.JS server, you only need Node.JS, nothing more. On the other hand, when you need a render-farm, you might have to roll out proprietary software, so you need an operating system on which you can install your software (IaaS).