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It's unknown. It's so new, few of them have over 100k yet. One guy who had his heavily modded and regularly took it to the Nurbergring had major engine problems at only 50k. Some here are highway cruisers and have 100k with few or no problems.
Historically, the 3-series have been generally reliable, but this one is pretty high-strung, and yours has the added complication of AWD, too.
A JB+ will probably be a little bit harder on your turbos and transmission. The 335is is basically the same idea though, so it won't be too bad.
It also depends on what "last" means. Any car can go forever if you keep fixing it. Many German cars are known to need some expensive repair and maintenance later in life...ball joints...bushings....cooling systems...window regulators & such. I've had to replace the cam bearing ledges on my car, which is the only internal engine repair I've ever had required on any car. That's concerning. The N54/55 also have pretty short con rods, which can lead to more stress on the bearings and pistons.
It also depends on how many cold start you get, and if you let it warm up before driving it hard. I never go over about 2300 rpm until the temp gauge starts to move, and don't really get on it until the temp is at 180.
Techron probably will help the injectors a tiny bit. It won't wash the valves though.
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