If this article by Autocar carries any weight then we should be in for a 4 door RC F...or a new IS F... Expect it to share platforms with the RC. Also a maybe could be we'll see convertible version of the RC F...
Following the GS F is likely to be a four-door version of the RC F, the IS F, which will feature identical underpinnings to those of the coupé but a slightly lower price tag. Expect to see the IS F "sometime in 2016", according to sources. This may well be followed by a convertible version of the RC F.