Is it possible to add a new window type using the Python API? It seems that it is possible to add new panels and regions but not new window types (editors) using the Python API. 
Is this true? And if so, is it possible that this could be added in the future?
Currently it's not possible, though it's been discussed a few times. Having custom PySpaces would be convenient, but I don't think it's officially on any roadmap.