Can I generate a PDF/X-3 compliant pdf via princexml ?

Not yet, PDF/X is on the development roadmap.

What's the current status of creating x1a and/or x3 compliant pdfs?

Currently we are focusing on support for PDF/A, eg. tagged PDF. We hope to get to PDF/X in 2013.

Are there any news about PDF/X-3 now that it's 2013?

It's closer! Prince 9 has support for PDF/A-1b, and that required some of the same metadata needed for PDF/X, like OutputIntent and document IDs. There are still a few things remaining to do though, which you can check by running Preflight on a Prince PDF in Acrobat.

Finally, the latest Prince alpha supports PDF/X-3 and PDF/X-4, which can be specified using the --pdf-profile option. Any feedback would be appreciated.