While I do understand Embree being a major improvement, I would re-state that it would make sense to take the current rendering engine, install the Embree subroutines in it, and offer it as a plug-in.

This makes some sense for me because,

1.  I'm assuming the Embree subroutines don't work on a system which does not have an intel processor.  Therefore, it only would make sense for people who could use it to pay for it and the other people would not have to pay for something the you couldn't use.

2.  Some people may not want to spend the money anyway and would like the option instead of being sort of forced into it.

Something else I'm curious about is that if there is enough passion for Embree, why don't you organize the construction of the plug-in and provide it?  Carrara has the open SDK capability to do this.  There's nothing holding people back from making it happen.  It would require finding a few people who can write the code, test it, and sell it.  Funding for such a venture would also be required but that could be organized as well.

-Kix