If you were in the ActiveE program, you may recall that the early version of software did allow Launch-mode. Not long later, issues started showing up with the motor’s output shaft’s gear teeth (splines, actually) and the gearbox’s counterpart were showing premature excessive wear and failure. BMW replaced the $30,000 motor in every ActiveE in the test program. Ow.
Soooo, I’m guessing that BMW is forbidding a Sport-mode until those high-torque low-rpm components are beefed up — probably in the next generation of motor, which may exclude the i3 entirely