Even if FDev were to create an Open PVE mode it is not clear to me how this mode should work. Turning off damage between player ships will be very artificial, especially since damage from/to NPC ships will stay the same. A PVE/PVP flag is similar, just optional per player. Those without a PVP flag are essentially invulnerable.
If the Open PVE mode is instead controlled by consent (i.e. you agree not to hurt other players) then who is going to enforce this when conflicts arise? This sounds like a potentially huge support job to me.
Instead, the crux of the problem is the pain suffered by those victim to involuntary PVP. What if, instead of artificially limiting conflicts between players, the pain of such a loss was greatly reduced?
Some alternatives:
1) If killed by a player, outside a conflict zone or a lawless system, the cost of your loss (ship and cargo) is automatically reimbursed to your account. This reimbursement could come from e.g. a community-driven fund, where PVE players do "insurance" missions to fill it. If indeed PVE player numbers are greater than PVP player numbers, the PVE crowd should have no trouble co-operating to outweigh the losses caused by PVP-ers. This adds some competition between PVP/PVE.
2) If killed by a player, outside a conflict zone or a lawless system, the cost of your loss (ship and cargo) is drawn from the killer's account. If there is not enough coverage, the killer goes into debt. Any earnings the killer makes from that point goes towards paying down the debt until cleared. This solution puts risk and burden on the aggressor, balancing it with the victim.
3) If killed by a player, outside a conflict zone or a lawless system, the cost of your loss (ship and cargo) is tied to the killer's bounty. When the killer is killed, the amount is reimbursed to your account. The killer can also pay the reimbursement to remove the bounty. This creates incentive for PVP-ers to hunt other PVP-ers, or for PVE-er to create a group of hunterers with the purpose of taking out PVP-ers to release reimbursements.
The point of these alternatives is to have a crime & punishment system that takes the victim into account, not just the aggressor. Tying these mechanisms to Power Play could, of course, also unlock many interesting competitions and tensions.