I meant integrating pcbmodelgen in KiCad source code, so there is no need to launch another tool. I am familiar with the Unix way and often appreciate it, but here IMHO it is not as elegant as it could be when integrated in the source code (e.g. see the code checking whether there is kicad2step executable present).
In my imaginary, perfect world there is a clean and stable API and all exporters are compiled to shared libraries, possibly out of KiCad source tree. Due to limited manpower we take decisions that get us faster to the goal, but not always through the most elegant solutions, therefore executing external tools is also acceptable. You asked me what I think, you get what I think;)