To fill the time before 10:00 am, here is what I think are the best and worst case scenarios from the unions’ perspective.
From the unions’ perspective, the best case is a full-throated reaffirmation of the Abood principles and a clear statement about why unions – which have a statutory obligation to represent all employees in the bargaining unit – are different from other associations (like neighborhood associations and the PTA) that don’t have such legal obligations.
From the unions’ perspective, the worst case is an opinion, probably authored by Justice Alito, that overturns Abood and finds that fair share agreements in the public sector amount to compelled speech (or compelled subsidization of speech). But, as in Knox, this opinion would then go further. In dicta, it would call into question the constitutional permissibility of exclusive representation in the public sector and invite the next round of cases challenging exclusive rep, again on First Amendment grounds.
Maybe things could go better or worse than these scenarios, but this seems like the basic range of what we could get.