On topic, will open only stop bots?
No, i don't think so, at least not directly. Bots will continue to do their stuff, and people diverting their attention to the bots will provide gaps for the player haulers. The bots will respawn and continue, and bots can work 24/7. If the bot epedemic is as bad as people think, then there is no way players can compete or take them down enough to matter.
What it would help with is identifying bots. It will take some time, and there would be false positives, so ulimately it rely on reporting to FD.
At this point it depends on your belief in FD to handle such reports. If, like Rinzler, you believe FD are unwilling or incapable of taking action against such accounts, then open only is not a solution to the problem, as nothing will happen to those accounts anyway. At worst they get a slap and a few days ban, and hey, they can always pick up a few more accounts in a sale to run the bots on.
If you believe FD do and will take action against such accounts, then open only will be a possible solution to botting.