You should be in good shape either way, actually. The same project
structure will work with either SDK version, so you can retain the
option to switch back and forth. The only "one-way" choice would be if
you start using the new UiBinder, ClientBundle, and layout panel
stuff. If you need to play it conservatively, you could hold off on
those things, but you can at least start using the new in-browser
development mode, which should make you even more productive as you
push toward your own launch.
Big picture, though, we're eager to finalize 2.0, so I wouldn't expect
too long an RC cycle this time. In other words, you should even be
safe to start using 2.0-only features in the timeframe you're
describing.