Quote - Very simply: No API

Instead of trying to play catch up to the state of the art minus a decade, were Smith or Daz to produce a documented API, you'd see one of the render apps for Poser in no time.  Any render engine needs an API to "talk to" a host application. No API = no way to talk to the application.

You can write integrations for 3rd party renderers. I wrote one for 3delight and one for yafray as hobby projects years ago. In fact, the yafray exporter is licensed under the GPL and anyone who wishes to extend or modify it or use it as a base for an exporter of a render engine of their choice is invited to do so. Go write that Kerkythea exporter, please. I'll be happy to help wherever I can.

3delight: http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=1364391
yafray: http://www.renderosity.com/mod/forumpro/showthread.php?message_id=1811598&ebot_calc_page#message_1811598