In the software development cycle, a release candidate is a release that could potentially be a final product. A release candidate can be used for production sites, but it is still possible that changes could be made prior to the general release.
For the time being the Joomla! 1.0.x release will continue to be supported and updated if security or other major issues arise. Eventually, support for the 1.0.x will cease, but this will not be in the near future.