A TDI is an economy car, just like a Cummins of Dmax is a tow rig. There are some people that are willing to go the extra mile and make big power, is it easy, no, but it’s achievable in the TDI.
350 to 400 hp is very achievable if you pay attention to the basics. You cannot make that kind of power and run the motor at 3000 rpms and expect it to have any chance of living. 400 hp at 6000 rpms is only 350 lb. feet of torque.
The stock crank needs a minor amount of attention, balancing, gas nitration.
Rods
need to be good aftermarket parts. Manley is going to release a TDI rod this fall.
Pistons
Diamond has a really good piston that has a excellent ring package.
Cylinder head needs lots of work,
Turbo, it has to be a lot bigger, and looser.
Cam has to be designed for the application, zero overlap, and big intake event, and short exhaust. The cam I used was 240 218 on a 118
Will this engine last 200,000; the answer is who expects any engine to last if you pushing it to the edge. Drive it sensibly and if will have good street manors, but remember it has a finite number of time you can push it.