Actually, compared to other companies in the space *cough*IBM*cough*, Sun's not moving quickly at all with certifications and product versions. Java's coming out with a version for SE about once every 18-24 months, and that's not horribly quick when push comes to shove.
I don't think that Sun's announced an exam for Java SE 6 - for starters, it's lower on the list of priorities than updating other exams, and as far as I'm aware, it didn't add all that much that they might feel needs to be tested in a form that's different than the Java SE 5.0 exam. Plus, there is a precedent for Sun's not having a SCJP version for a given version of Java - they didn't have one for 1.3.
And, finally... my company moved from 1.4 to 5.0 only about a year ago. I don't think we're going to end up moving to 6 any time soon, so I'm not sweating the details. If you're really worried about keeping current, I'd look towards the 5.0 upgrade and take that.
Theodore Jonathan Casser
SCJP/SCSNI/SCBCD/SCWCD/SCDJWS/SCMAD/SCEA/MCTS/MCPD... and so many more letters than you can shake a stick at!