I don't think a neo-Supra will be based on any F1x chassis. That's just way too large.
I think we are going to see something all new here. The words were "will be a sustainable sports car with environmentally friendly technology". That sounds like a i6 or something of that nature - definitely an "i" brand vehicle. And then perhaps toyota will repurpose the chassis for a Supra, Celica, or MR2, using a more conventional powertrain.
2008 Interlagos Blue E93 M3 - M-DCT
2011 Salsa Red Jetta TDI Sportwagen - DSG