WordPress Development is now released publicly. I think that it's the time to migrate all the questions related to WordPress (tagged as wordpress, wordpress.com) to WordPress Development.
Can't be done yet. Questions cannot be migrated to or from beta sites. This also applies to migrating between "real" sites and the betas.
The rationale is that the beta sites are not permanent yet, so there's no point migrating questions over until the sites get out of beta.
Jeff Atwood provided some detail in a recent answer.