I'm not sure you fully understand the automotive market.
The 86 already does that.
Indeed. And it's $26k.
Now I can't really afford any brand new car right now. But I certainly can't afford a $26k+ one, which is what an FRS goes for. Or if I use my own UK market, I'm more likely to be able to afford a £18.5k MX-5 than I am a £24k Toyota GT86.
And if I was Toyota, I might even look at the success Mazda has had selling relatively affordable Miatas in the past, and the relative lack of success it (and Subaru) has had trying to shift the 86 in most markets, I might be tempted to nudge in on Mazda's territory with something more affordable.
That is this car.
edit - and why take a risk with a car that's untested and looks like a catfish instead of the best selling sportscar of all time?
Well as this thread has already established, at least as many people like the look of the car as those that don't - so from our small sample there's at least 50% of the driving enthusiast market covered. I'm a huge MX-5 fanboy but if Toyota made one of these and sold it for a similar price, I'd have to think very, very hard about which one to spend my money on.
Secondly, I suspect this isn't just a bolt from the blue. If Toyota is entertaining the idea of actually making this, then I imagine they're not going to develop a whole new rear-drive platform for it so shortly after co-developing one with Subaru.
There are rumours flying around that Toyota will be sharing the MX-5 platform at some stage. There's also a high-profile technology and development collaboration with BMW on the go. And I imagine they'd be open to the idea of improving the GT86's economies of scale by using some of the largely bespoke solutions they've developed for that car. If this thing doesn't use one (or a mixture of some) of these methods, I'd be very surprised indeed.
Thirdly... why the hell not? Even if you don't like the way this thing looks, I can't fathom not seeing a point to it whatsoever. Most car people I know would crawl over broken glass to have more affordable rear-wheel drive cars on the market.