When you start to use WordPress as an application platform, one thing is very soon clear: WordPress defines very little base structure for your application code, where to put and how to write tests, how application is loaded, or for example how dependencies should be managed. Because of this, applications or just complex sites built on top of WordPress tend to get really messy.

There are application frameworks built on top of WordPress, but none of them seem to have wide enough use for to build any serious applications on top of. Until any of those gets wide-spread adoption, combining existing, non-WordPress specific PHP technologies as a custom solution probably is a more future-proof solution. We will be looking into one possible stack of technologies.