I asked this question on Dec 11 '13 and now this question is no longer valid.
Some of the important dates for JDK 1.8 -
2013/09/05 Developer Preview
2014/01/23 Final Release Candidate
2014/03/18 General Availability
Will it be safe to start development with JDK 1.8 in a commercial product now? Though, it's still in developer preview phase, definitely be for testing purposes. Or should I wait for it's general availability release?
In future, main issue will arise when systems get updated with newer releases of JRE's and then some of the API will be deprecated if development starts with JDK 1.7. This may tend to misbehavior of the system processing.