IMO the HUD is an accident analysis red herring.
The combination of no necklace and solo diving was the key issue with this dive. Any multitude of issues could cause a need for immediate bailout and it's not the HUD that interfered with bailout deployment. If they were unable to deploy bailout effectively then that would have been true with any event that impacts mental faculties or a situation involving entanglement, etc.
The solo aspect I think comes into play in terms of mental state and bailout deployment. The need for complete and total self rescue capabilities even when mental faculties are compromised, makes a necklace or BOV an absolute requirement for solo CCR overhead diving. When you're confused from CO2 or hypoxia, or if your 2nd stage is entangled, if you don't have a buddy to help notice your altered mental state or assist with bailing out, you still need to be able to self rescue. A necklace or BOV with an already open valve seems the best way to ensure you can bailout even if you're down to two functioning brain cells.