So the new back end is finally merged into the master branch. If you update your own installation you need to install the affine Python module which is available both via pip but also in most distributions. Cairo is no longer needed. This should make installation on Windows much easier.
The SVG produce by the new back end is also much better than the old one. Artifacts like repeated moves are filtered out and the outline of parts is much more continuous. The weird inverted arcs in inner corners are - for the most part - replaced with smooth Bezier loops. This should reduce acceleration in the corners and allow for faster cutting.
I am still pondering whether it is worth adding a native DXF back end. While there is only very few commands needed by Boxes.py the format does not look like fun. I am also scared that it won't support the text the way we might need. For now the output still uses pstoedit for converting to DXF.