The original 64 Mustang was designed with IRS, but from a price perspective it didnt make sense. So they used a cheap Falcon axle. Having IRS is awesome. Drive an early 2000’s Mustang with IRS next to a faster, stronger GT with live axle. I guarantee after that drive what you want is the power of the v8 with the IRS.
The only downside to IRS I’m aware of is cost/complexity. When done right/beefy, they are killer. I think a lot of people just don’t understand them for performance applications.
Sure, drag racing is one thing when you have monster slicks and a ton of bite, but the reliability gained comes with a huge penalty in all other scenarios. Like I said above, the off-road racers perfected the beefy IRS in brutal conditions. 400 HP to the ground on 37 in tires puts incredible stress on IRS components - far more than a drag car. But that IRS helps the vehicles so equipped out handle their solid brethren. In the late 90s, Ivan Stewart’s Toyota Trophy Truck regularly beat up on the Solid trucks with far more travel. Of course that was all custom gear, but the principle applies.
It can be done with modern tech, no prob. I just think the real hurdle is in the traditionalist mindset.