Please allow me to introduce myself, I'm Howie Bernstein the ClearCase and ClearQuest product manager. Right now we are in an open beta with two significant features for ClearCase and ClearQuest. ClearCase is in beta with Role-based Access Control Lists for ClearCase elements, and ClearQuest is in beta with Multi-record update in ClearQuest Web (as well as a few other features). If you are presently a ClearCase or ClearQuest customer, you can access the open beta here: https://www14.software.ibm.com/iwm/web/cc/earlyprograms/rational/cacv801/
It would be a mistake to think of RTC as a replacement for ClearCase and ClearQuest. It would depend entirely on what features of ClearCase and ClearQuest your organization depends on. For organizations that make little use in ClearCase of dynamic views, process triggers, build auditing (and others) then perhaps switching to RTC SCM would be a reasonable consideration. The same can be said for ClearQuest. If your organization takes advantage of the advanced customization features of ClearQuest and depends on those features to execute your custom workflow, then RTC might not be a good solution for you.
In our development organization, we use all three, together. We use ClearQuest for external RFE and APAR submission and workflow, we use ClearCase for our SCM (on the ClearCase and ClearQuest teams, as well as other teams throughout IBM) and we use RTC for our work item planning and execution. We have excellent bridging and synchronization capabilities between CC/CQ and RTC that makes this possible.
As to the future, we have development teams working on new features in both ClearCase and ClearQuest and we plan to introduce new versions in the future.