Generally, the toolbox is from the very beginning on designed to be as modular as possible. Nevertheless, currently, there are still a few more general things to be solved to end up having a truely modular design of the toolbox, allowing for easily writing modules.
A few rather practical aspects of writing submodules for the toolbox can be found already at the respective page. Whereas the cope of that page is to give a tutorial in how to write actual submodules, this page is designated to the overall concept of modularity.