That's an interesting point of view, but, I'm not sure how you're coming to those conclusions. Cars are fast these days because of technology, and the market wants it too. Yes, the Hellcat is tunable, people have modified them and tuned them already using aftermarket software on the stock computer. What about the G8? It's basically the same technology as the Hellcat engine without a supercharger. You can tune and modify both cars almost in the same manner. It's up to the customer to decide if they want more power. A stock Hellcat may be plenty for the owner of that car, power to them if that's what they want, and well, if they want more they can pay for it. If you're talking about "last call" because you think electric will take over, you'll probably eventually be right, the Tesla's are pretty neat. But it'll be a while before that happens, and I'm not against the changeover to another type of engine, but there's still going to be some time for gasoline engines.
What do you mean it's out of the tuner's hands? Tuners/builders have always made what they could and outsourced the parts they couldn't do in house, or parts that are just more cost effective to do that way, what's the big deal with that? It's not cost effective to do everything yourself most of the time. But, I mean, the GTR is a heavy car, and it's pretty fast stock, but of course it's going to need stronger, aftermarket parts if power out put is raised by 3x, 4x, 5x or more. That goes for every car, regarding engine internals or driveline components. Unless you're one of those few ultra in house manufactures like McLaren, you're going to be buying the correct parts from different vendors and installing them in a build (and I'm sure they have to get parts from other people too, everyone does). Who would want to try and build pistons for their 2J when you can just buy bad ass ones from JE or whoever already? This is how it's always been. Well, except for the old days, but that was a while ago. As long as there is a market for it the aftermarket won't go away. And cars are getting quick now. 2000WHP cars you can drive on the street are... kinda common now. Stock cars running 10's or even 9's happen now, it's insane, and I love it!
Tuning is not an issue on most applications, again, as long as there is a market for it a company will invest to create some type of system for it, there are plenty even for the GTR now, the Motec being one of the leaders in that, but there's Syvecs or heck you could even use a Cobb to flash the stock computer, which is fine for most customers and it's not all that expensive either. That's just an example of one application but of course there are cars like the ISF that no one has been able to tune, and that's because, yes, it is complicated, but I promise if Enough people needed it a company would invest and figure it out, and then sell it. That's what I think about it anyways.
Street cars are faster than they have ever been.