The article starts and ends with "they are very different tools for different use cases". What was even the point of writing the whole thing hypothesizing whether one will replace the other?
Author here. It's titled this way because Docker seems to come up in a lot of discussions around Nix and is often compared with Nix. Partly because of their overlap in functionality but also because people may not understand the difference between the two.
The goal here was to a) highlight the different use-cases between the two tools b) compare the tools in the areas that they overlap and c) show how both tools can be used together.