The HUD is very accurate,
but is the human? … and what about duplication, monitoring?
Using a single self-monitored HUD raises the question of how to monitor the human derived output. Use the other pilot and head down instruments, or with two HUDs, what if the humans disagree?
The automation issue is not what can be automated or at what cost; it is what should be automated and what reasons drive this decision. For the latter it is often the limits of human performance, the ability to conduct a task, or the reliability of the task in a range of conditions or over time.
Current installations usually have only one HUD on the captains side. Since the captain has to fly low vis landings anyway that kinda makes sense. Future HUD installation will be dual, for example it is standard equipment on the 787.
The fact is humans can fly precise enough to ensure landings nearly every time they try, the majority of all landings is done manually and only very few of them go astray. During low vis the issue is missing visual cues for a normal landing, however if those are artificially supplied by other means, in this case the HUD, humans are perfectly capable to their usual good job.
Sadly i did only my initial typerating on a HUD equipped 733 and haven't flown a HUD since, however during training with the HUD it was basicly a non-issue, the PM by default was the RHS and monitoring was not an issue, of course callouts if somethings doesn't fit, but that is something we do every day anyway, so nothing new there. If one of both calls a go-around it has to be performed, haven't flown in an airline that doesn't apply that principle in normal operation in the first place.