You've made me think, what if Toyota does know they can't just bring back the Supra?
Your comparaison to the NSX is spot on, but there is a difference between that and the Supra. The NSX had always had one generation, with not that much difference between the first car from 1991 to the last car from 2005. That's 15 years of the NSX being, in essence, the same car.
The Supra, on the other hand, had various generations, and a shorter life cycle between them. Of course, this ended after the Mk IV as there never was a Mk V. Now it is late to make one without it being compared to its direct predecessor, and of course generally disliked for not "living up to expectations". And while there's a possibility Toyota didn't realize it, I'd say they know. And they made the Mk V anyway.
Now the Mk V is disliked. And most people dislike it for, simply put, existing. And what if that was it's purpose? What if Toyota wanted to bring back the Supra, and decided to pretty much sacrifice its first new generation, so that the next one, the Mk VI, has a smooth road ahead of it? It's possible that by that point only the hardcore, blinded Mk IV fanboys would complain about it. Everyone else would just move on and accept that the Supra is just a name for a sports car, not the specific car that the Mk IV was. So the car would have the reception it deserves, good if it's good, bad if it's bad. No unrealistic expectations, no unnecessary hype, nothing to really kill the car before it's born.
I'm not very knowledgeable in all the things I'd need to be in order to know how realistic that is, but I certainly hope it's the case.