Interesting question. Need a Bmw Tech to answer that 100%. I would want to rule out a bad key as you've gone advanced down that route.
I would also be asking myself:
Battery voltage
Could this car have suffered a no code charging system failure on freeway causing low fuel pump voltage before shutting off. Am I seeing a higher voltage now after battery recovery.
Do I have good battery ground and charge cables
Has DME caused No charge or has alternator/harness shorted a DME driver.
Or can I rule that out because it simply due to customer/tow truck driver/simply worn out
No start
Can I verify power and control with DVOM or Scope at coils during cranking
No codes
Why no manipulation or communication errors in CAS after all the start attempts.
Can I unplug sensors to generate some.
Can I put all the modules to sleep, check parasitic draw while asleep.
Am I getting good power and grounds on suspect modules.
Do I have a short in a harness.
Good luck