Here is what I know....
The issue is engineers basically want to beat the living crap out the Z and the competition for the money, from power to handling. Toyota has watched as the Z has done a great job proving a sporty halo back to the brand.
So this is why its taking so damn long
1. There are Supra test mules based on the IS RWD platform, which actually is from the Lexus GS platform. It handles well but it is heavy, being shared with luxury sedans.Engineers are not totally happy with the results. Thing is, money is saved.
2. There are Supra test mules based on a NEW Supra only platform. It handles GREAT and is light. Thing is it will cost a fortune to sell if Toyota wants to make money on it. Now Toyota is big enough to sell at a loss but that is not profit thinking.
3. Looks. Tons of internal debate on what the next Supra should look like. Too many different renderings to show.
4. The engine(s). Well unlike the Z, it does seem 2 engines will be available. THe first being the 3.5 in the IS WITH the dual VVTi and direct injection. Toyota 3.5s do without the direct injection in the Rav-4/Camry/Avalon, thus less power.
I have heard around 320-330hp.
The optional engine would be the Lexus 5.0 V-8 coming from the LS 600L h. This engine is also going in the IS-F (super IS). 415hp, 8 speed auto
5. Toyota has a 8-speed which would cut costs but enthusiasts would puke. So they need a high HP handling manual or DSG gearbox....

And I'm donE!!!
lol