Moving on from @Low Rider and the thread on the end of the Z4 there looks to be the Toyota tie up but the first new roadster to come from the group looks to be going to be the Mini so no replacement for the Z3.
Quick vid of it at a 2014 concept supposed to be produced for 2018/19
View: https://www.youtube.com/watch?v=8ugq7AWqBQ0
Quick vid of it at a 2014 concept supposed to be produced for 2018/19