The next release of the ArcGIS Viewer will be 2.1 - this will be the first non-sample, non-beta version. We are not planning a "2.0 final" version.
The 2.1 version of the Viewer will be based on the 2.1 version of the API. We plan to release both of them around the same time. With the caveat that plans can change (and often do) ... currently we are aiming for a 2.1 combo release at the end of September.