The main reason I wouldn't want a rear radiator on my car is that is where the trunk is and a radiator back there would reduce it's utility. Also, the long piping could have reliability or cost or some sort of drawbacks... although if there were extruded aluminum heat exchangers running here and there under the car, perhaps the radiator itself could be eliminated??? Then there is my pickup- for sure I don't want a radiator anywhere near the tailgate; it'll get smooshed, or the load will obstruct the airflow, or something. On Moon Unit, the wagon, there aren't any good places for a rear radiator either.
Now, were I to modernize my Corvair with a liquid cooling-medium engine I would probably pursue a rear radiator location as there is no trunk in the back for a radiator to interfere with. I find it odd that the Corvair is popular for mid and rear engine, liquid cooling-medium conversions and yet 100% of them go with a front radiator.
I should point out that even though I love my rear-engined vehicles, they are saddled with a built-in reduction in utility as stuff-movers, in that anything put into their front trunks really, really needs to fit properly and the lid be fully latched down, whereas in contrast, you can let a rear trunk lid or hatch stay open for oversized cargo to stick out of with little bad consequence. Even better yet is the ability on some cars to fold down the rear seat for more cargo room- not an option with a front trunk. Additionally, weight variations on the rear end of a front wheel steering vehicle (from empty to fully loaded to even substantially overloaded) have a relatively minor impact on handling whereas having the trunk on the same end as the end that steers makes the vehicle's handling exceedingly load-sensitive. Furthermore, having the trunk on the same end as the steering wheels forces the trunk to be smaller within the same size exterior envelope because the wheelwells intrude further into the trunk space because the wheels have to turn (not rotate) for steering. So, I reluctantly have to say, front engine front drive is where it's at for max utility, safety, and efficiency.
I do believe the VW 1L could be front engine fwd with no performance penalties, and then they'd have a rear window and hatch or trunk as well.
Interestingly enough, this latest 1L, in spite of having the engine towards the rear, has the radiator up front!