The release date for the official release is not yet decided and I cannot provide the requested information. Nevertheless, RadEditor for SharePoint 2010 and other AJAX controls available in the CTP are official and stable products and you can use them without problems under SharePoint 2010. The AJAX controls are also available in a separate official installation for SharePoint 2010 (Telerik_AJAX_Controls_For_Sharepoint2010_2012_2_724_Dev.msi), which you can download from your account.
the Telerik team
Learn how the Telerik controls can be integrated in SharePoint 2007/2010 from this resource
. To watch them in action, explore our online SharePoint 2010