Reaction will be updated to Gantry 2.0 in the coming days. Technically Gantry 2.0 is backwards compatible, however you won't get any of the new 2.0 features by just dropping in Gantry. There's still some work required to 'activate' the features, and also RTL support means a bunch is done by the framework, but still 75% still needs to be done by CSS which means custom work required.