This is a classic case (as reported in the news) of a minor malfunction leading to a significant safety event.
Malfunctions leading to a failure of a starter motor are anticipated and layers of minimization incorporated. Even the uncontained failure of a starter motor is anticipated and its consequences minimized and/or mitigated, including the penetration of a fuel system, leakage, ignition and subsequent fire. However since there are numerous malfunctions of powerplant systems that can result in a fuel leak, ignition and fire, the critical system that are anticipated to work a high percentage of the time are fire detection and fire suppression.
In my view these are the most serious lapses of all in this event and must be addressed at a much higher priority than all the rest of the findings/recommendations. Unfortunately the NTSB political appointed Board members have a tendancy to meld all their recs together and promote those with the most news worthy appeal.