The short answer could be: Why changing something that works?
As far as I know, there isn't any other open source renderer programmed in Java so proposing other renderers in Sweet Home 3D is quite challenging. Anyway, you could try the rendering plug-in based on YafaRay released a year ago, and if you wonder why choosing YafaRay, please read this article.
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Emmanuel Puybaret, Sweet Home 3D creator
