FYI. In respect of filters in Apache, there is an intention of making some improvements to mod_python's support of filters and also its interaction with mod_include (SSI) filter module.
In terms of server side includes, the intention is to allow Python code to be usable within a file passed through mod_include, much like how it can already be done with mod_perl. This would be more efficient than the current need to use "include virtual".
One could also explore whether a means could be provided of allowing whole new element tags to be defined where the callouts are implemented and processed within the context of mod_python.
From what I have seen at the moment, people using mod_python don't tend to use filters much at all. This is possibly partly because of mod_python's inability to dynamically register filters, or more likely because there isn't a good appreciation of how Apache filters could be used. But then, at the moment, some parts of mod_python don't even play nice with predefined filters like CONTENT_LENGTH.