I have been thinking about implementing the MovableType xmlrpc API for LifeType. I have been getting a little annoyed with the metaWeblog api, since it doesn't have seperate fields for the main text and the "more" text. LifeType works arounds this limitation currently by using a special string to indicate the different text fields.
It is pretty easy to implement the newPost API, as the client just has to set the additional fields. On the server, if the fields are set, it knows that it is a MovableType client, and not a metaWeblog client.
The problem is with the getPost API. The client passes the same thing to the server when using both the metaWeblog and the MovableType API. So if you want an implementation that handles both, the server will not know what fields to return. The server implementation can not fill out both fields as either the client will only see half of the data, or it will dee duplicates of the data.
This seems like a poorly designed API. The thing that would make this work is if the client could pass an additional boolean to indicate if the client is using the MovableType API.