Supported Platforms
You can build Read It Later applications for any platform.
The only exceptions to this revolve around Read It Later's existing native applications for Firefox and the iPhone/iPod Touch. You can build applications for both Firefox and the iPhone, however in the case of these two platforms, they should not be full Read It Later clients that directly compete with Read It Later for iPhone and Read It Later for Firefox.
If you have any questions about this, the easiest thing to do is to contact me.