I'd like to extend Scribus using Python, not just automate things with it...
Currently, that's not really possible. There is work on making it possible to extend Scribus with Python to some extent, especially the GUI. It's now possible to use PyQt to write your own palettes, but you won't be able to use custom Scribus widgets or get into the innards of the application. The Scribus core is unfortunately not well suited to extension from Python. More advanced or tightly integrated extensions are probably better written as C++ plug-ins.
Stop learning proprietary languages and memorizing template tags. Symphony leverages open standards like XML and XSLT, and good old XHTML and CSS. Even the admin interface employs the widely-used jQuery library, so extension developers don’t have to learn a whole new framework when extending the back end.
D. Johnson, and T. Jankun-Kelly. Proceedings of graphics interface 2008, page 163--168. Toronto, Ont., Canada, Canada, Canadian Information Processing Society, (2008)
E. Bakke, D. Karger, and R. Miller. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 2541--2550. New York, NY, USA, ACM, (2011)
E. Bakke, D. Karger, and R. Miller. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 2541--2550. New York, NY, USA, ACM, (2011)