I think it's more an issue of how Toyota wants to position and market such a car. The unfortunate reality is that even in today's dollars, a $40k Toyota is a tough sell. Just look at the GTR as a good example - everyone loves talking about how great it is for the money, but Nissan can't sell them. A big reason it that people don't want to pay $70k or $90k for a Nissan. (The 370z's lagging sales in the last year show that people don't want to pay even just $40k for a Nissan either.)

So IMO it just comes down to how Toyota feels about expending R+D and marketing on a midrange sports coupe like the Supra that probably won't make money, and how they feel it will build interest in the brand as well as performance image for the brand. There are certainly other options I could see that do the job better, especially since the FT-86 already exists.