Correct, Ft-1 Design concept is totally irrelevent to the Z4 story. Bmw/Toyota partnership involving the Toyota Hybrid System II is over 3 years old now, and without doubt they will release a vehicle but as said countless times in the press and media, and by toyota themselves, this will not be a replacement for the Supra. Dezi Nagaya said in an interview regarding the GT-86 that any new true toyota sports would be powered by a gasoline engine and not a hybrid when he talked about the 3 future vehicles - the small sports car, the medium (gt-86) and the larger.
On another interesting note, back in 2007 there were 2 concepts commissioned by toyota from Toyota's Europe Design Development ED2 and Calty Design (FT-HS) - Toyota eventially took its styling cues from Calty for the the ft/gt-86