The fact that they've stretched the MY 2015 F10 production to 16 months, ending next November would seem to confirm that the G30 will go into production right about then. If true, it looks like it should see very early 2017 availability.
Similarly, the shortened Z4 model year would appear to suggest it's replacement is coming early next year. Edit: Apparently the Z4 may go on hiatus for a few years.
http://f80.bimmerpost.com/forums/sho....php?t=1100742