Now that RC1 is available, we'll be focusing on 1.6 compatibility. It's not there yet, but we think the changes should, overall, be minor from an initial standpoint. I can't give a timeframe, other than to say compatibility will not be with the 3.1 release later this month. We're gunning for one of the point-releases after that date, which could be January, but could also be in February.
The biggest development issues with Joomla 1.6, that we're aware of from a preliminary investigation, will be creating the proper user. Initially, we plan to register all users as the default user (similar to registered in Joomla 1.5). Eventually, we plan to let the admin select a user type that Facebook users' should become upon registration.
Hope that helps. It's somewhat intentionally vague because we don't want you to rest your hopes or make promises to a client based off of our timeline. Joomla 1.6, in general, will have bugs in the first release. Always be careful when jumping into a new release!
Finally, it wasn't asked, but there will not be a separate subscription for JFBConnect on 1.5 or 1.6. The same subscription would provide access to both releases.