Given the reliability of the entire of the N54 (HPFP, Cams, seals, injectors, VANOS solenoids), the turbos aren't the only thing I'm worried about.
Based on what others seem to have been able to accomplish for "miles tuned", I'd bet the turbos are less likely to fail from being daily driven on a 15psi map (occasional romp on freeway ramps etc) than the other parts mentioned.
I'm not in the know enough to comment on likely success of a new flash but the available ones for the N54 do seem to have their issues. It seems this DME has more tricks up it's sleeve than a vegas magician and prodding it with a flash to do what you want is no easy task. (the logic is insidious).