You have argued that Open-PvE is impractical, but I think you consider an over-complicated implementation; FD would be more likely to make it simple. The game already tracks the origin of all damage so that bounties, combat bonds and notoriety can be assigned. So all that's needed is a check like "if source=CMDR set damage to zero". Even the source of collision damage is already tracked: the other day I collided with someone in the mailslot at Jameson, died and was told "X killed you".
Yes, there would still be griefers. Creative people would come up with ways to disrupt gameplay in the mode. But now it would be clearly unintended and FD could punish the behaviour. There wouldn't be straightforward ganking (gankers would stay in Open) and the few remaining griefers could still be blocked.
Those punishments would still be after the fact though, as I described with my example of being scanned in a station that's no better than what we have now with community solutions (eg Mobius private group, others are available).
Open PvE is an impossible ideal to work towards & would create extra work for FDev staff that is currently done by the community for groups like Mobius. I don't think FDev would be very motivated to cover that workload and potentially arbitrating misunderstandings (cynical or genuine).
I play in Open, I don't seek out PvP I do get shot at sometimes & roll with it. The way I approach the game means I get the upside of maximising the possibility of meeting strangers without the downside of being concerned about being directly attacked ie the two primary goals of any Open PvE proposal as I understand it. It works for me. Others may prefer to play only with friends (or other like-minded players) and private groups were added for them.
If a player is wanting to maximise the chances of seeing other players inevitably one must accept that not everyone they meet will be nice to them, or have the same motivations. If they are unwilling to avoid putting themselves into situations they know they won't enjoy why should they expect others to do that work of keeping them separated?
On a personal note I rather like that when meeting a random stranger in Open both parties are usually initially wary of the other. Splitting Open into 'definitely up for a fight' and 'definitely not going to shoot at you' would remove what I consider to be a core part of the multiplayer experience. I appreciate there are those that would rather be sure but the game does already cater for both camps without FDev needing to do any work at all
I agree a partial implementation of an Open PvE mode is workable, imo we already have a good enough solution with (imperfect) PvE Private groups. A 'perfect' PvE environment is impractical imo, as I described before I think there would be an unending list of rules to keep adding.
So what's the problem with Private groups that an Open PvE proposal is looking to solve?