In looking at the APIs, there are a couple of APIs I'd like to use, except that they don't exist:
First, there is a SET AVATAR, but no GET AVATAR. This would be nice.
Next, there is a way to start video in a call, but no way to control the whether the video is in the Skype window, a separate window, or fullscreen. There is also no way to set the position and size of the video window. This would be helpful too.
As it stands, you can write an app that looks like it is the chat client, but you can't do the same for video. Ideally, you'd be able to hook the video to a window in the client appliction (to avoid the focus problems that come from having the video window owned by the Skype process).