I have a silverlight app that I want to support plugin development for. I'm thinking that the plugin developer would create a dll and my main silverlight app would have some sort of config file that you would list the dll and type of the plugin, and the main app would detect, download, and load the dll for the plugin.
Does this sound possible to do with silverlight?
What would be the best approach?
Sounds like a feasible to me. I'd probably create a set of interfaces for my plugins and provide those in some kind of development package for plugin developers. As for loading assemblies dynamically at runtime in Silverlight, check out this link:
Think about storage too. I was thinking about this same curiosity. Perhaps IsoStore is a place where you can keep them. A user has a plugin for your app (that conforms to an interface) and you can have them locate it (OpenFileDialog) and load it into your app (save in IsoStore). It isn't a durable solution of course, but an interesting one.
Have a look at the Composite Application Library: http://compositewpf.codeplex.com/
This frameworks helps you to create a moduled Silverlight application. Using this frameworks you could add new modules with ease when you are familiar with the framework.