How can I render SVG output (and other MIME types) from my workflow?

You can add multiple mime types to a workflow output port (to be used by the output renderers) by selecting the output and going to "Metadata for 'myoutputport'" - under "MIME types",

eg for SVG add: image/svg+xml

This should enable the SVG renderer for the output port. You might need to right click on the value in the left hand column and select "SVG" instead of "Text".