We're tentatively hoping to have the new Admin done by the end of this year as a conservative estimate, probably even sooner if possible of course, but we won't rush it into production before we're sure it's truly done, fully tested, and properly sorted out.
Initially, we're just shooting for feature-equivalence with our current Admin, to keep the project scope focused and prevent feature creep that would just set things back further. Once that goes live, we can start modifying the new Admin as needed to add any controls and settings necessary to support new features and functionality.
That said, we are at least taking the opportunity to make interface usability improvements (without changing things too radically) and remedy some inherent limitations of the current Admin -- e.g., since we won't be limited to a fixed Flash applet size, we can consolidate settings that currently span multiple, sequential panels (such as product configuration and shipping settings) onto a single, larger screen (i.e., no more Next buttons! :^).