I mean Sunflow's last update is from 2007....

You could also use YafaRay with their XML interface:
http://www.yafaray.org/
http://www.yafaray.org/development/docu ... n/XMLspecs

Or use POV-Ray:
http://www.povray.org/

Apparently an API is already there/possible:
https://platform.netbeans.org/tutorials ... ray-5.html

Or Blender (by using their Python interface..jython?):
http://blender.org/

Just think about it, a new render system would definitely boost sweet home 3d to the next level!