Exactly what the head wrench at my Kubota dealer told me. The issues with the T4 finals tractors arise when owners don't follow the owners manual concerning engine operation. He said EVERY repair he's had to make concerned early shutdown during regen or over riding the regen numerous times.
Of course mot 'adults' today are poor at following instructions or never bother to read the owners manual in the first place.
Despite that, I'll still never own a T4 final tractor, simply because I don't want or need some joe college engineer telling me a T4 engine is better than my post 3 engines. I don't buy that, never will.