I purchased Elite Dangerous in February. After suffering some attempted ganks in the first week before I could afford anything or even knew how to play, I switched to Solo. It makes sense to switch back to Open only after you have SO much money that losing a giant amount of ship insurance is no big deal. I could easily go back to open right now with a cheap ship, like a Cobra, but it'd sting to lose my Federal Corvette to a gank wing... and what's the point? I haven't met people to wing-up with, and I can earn massive money completing wing-missions by myself.
Those who want to gank everyone and talk about it being an important part of the game have the advantage of going into OPEN with:
1 - Years and years of practice
2 - The best possible combat build/wing they could manage
3 - They may/do go against builds designed for other things, that could never fight off or escape an engineered PvP situation. Even if you make a mining ship that can handle low level combat, you're not going to be min/maxed like someone who has only designed their ship to kill you.
You could have a game where everyone is forced into open if the penalties for being a were more severe. As it sits now, the penalty for someone costing me 24,000,000 in rebuy is the same as when I accidentally shoot an NPC civilian who later dies. Notoriety is a pain in the butt, but it's the same for accidentally scraping a system authority vessel who later dies from another attack as it is to purposely wait near a burning station and kill everyone who comes out.
As you said...
A - Notoriety for killing players should be different somehow, perhaps based on the player's ranks and the value of the ship destroyed.
B - Warnings could exist about where those notorious pirates are located (as you said).
C - Perhaps incentives or areas or awards could exist for players that are specifically dangerous and worth doing... so those who want to PvP or those who would risk PvP for a bigger reward... could sort of have their hot spots.
What if some kind of "open only" PowerPlay incentive was tied to anarchy systems?
What if certain systems were only available by "open" System Permit... perhaps a pristine ring system... things like that.
They could pinpoint or update "pristine anarchy systems" between PowerPlay capitals and put some kind of activity... like...
"Each power races to mine the most X in <System Open Only>... conflict zones are breaking out all through the system. This boom rush is occurring in a dozen systems located between all of the powers."
They could set this up in asteroid belts if they want to, as they are valueless and nobody ever visits them for any reason that I've heard of, so updating the game to put content in the belts would give players a reason to play PvP, a reason to do Powerplay, and it would even allow Solo players to feel safer dipping their toe in open as long as they stay away from the shark infested contested spots, as the ganking commanders would suffer a lot stronger penalty for bullying up a Hauler with their fully engineered Anaconda.