The best platform and language neutral advice I can give is this:
Design your entire app around the plugin SDK.
IMO, a plugin SDK should not be an afterthought. If you design your app to basically be an empty shell which loads plugins, then the core features are implemented in your own SDK, you get the following benefits:
- High modularity of components, and clear separation of purpose (it kind of forces your architecture to be good)
- It forces your SDK to be really good
- It allows other third party developers to make extremely powerful, core-level features as well
- New developers/hires can easily start work on a major new feature without having to touch the main app - they can do all their work in a plugin (which prevents them screwing up anything else)
In C/C++, you probably use dynamic link libraries and either function pointers (C) or interfaces (classes solely consisting of pure virtual methods, for C++). However even if you use Javascript, I'd still recommend the above architecture.
