I think pretty much any modern vehicle can go 300-400K without too much difficulty. Most engines today easily last that long, or much, much longer. Better oils, cleaner fuel, better manufacturing, precise FI, etc, all mean engines are much more long lived than a few decades ago.
Transmission are more of a crap shoot. The move to cramming a lot more speeds in AT boxes actually saw a drop in reliability, but I think designs are getting better. The jury is still out on CVTs with the exception of the planetary system Toyota uses in the hybrids. As we tend to keep our cars for a long time, I was pleased that Toyota had kept their indestructible four speed for the 10th gen Corolla.
The stuff connected to engines has become the "straw that breaks the camel's back." On some BMWs they have plastic water pumps that are not only hideously expensive to buy, but seriously buried and cost a fortune in terms of parts and labour. Sensors and HVAC systems and other parts can not only be unreliable, but very, very expensive. That's why you usually see the very high mileage cars coming from the group of simpler machines like Corollas, etc. They don't typically have sub-systems that can cost many times the value of the car to repair. That easily happens on more complex cars as they age. Those lower end cars tend not to have turbos. Their engines are not stressed highly. They usually have simple suspension systems that are easily repaired, and thanks to high volumes, by the time parts are needed, they're very inexpensive.
