The number of packages to extend the functionality of R is immense already, and climbing. On one hand, we want to encourage you to write plugins for even the most specialised tasks you need solved. On the other hand, the average user should not get lost in huge menu trees full of unknown statistical terms. Therefore it seemed reasonable to keep the plugin handling in RKWard quite modular as well. The RKWard team maintains its own public package repository at http://files.kde.org/rkward/R, designated to host your external plugins.
As a rule of thumb, plugins that seem to serve a widely used purpose (e.g. t-Tests) should become part of the core package, while those who serve a rather limited group of people with special interests should be provided as an optional package. For you as a plugin author it’s best practice to just start with an external plugin.