I myself dont like PVP. I just think that having different modes breaks some of the games intended mechanics and somehow creates an unfair advantage for Solo Players i.e. Power Play. I just think there are ways to make Open Only which doesn't force anyone to engage in PVP if they don't like it but rewards players who are bold enough to go through risky situations involving PVP. Because of the game modes, human piracy, bounty hunting, stealth gameplay and powerplay are not effectively implemented and balanced because of the mode switching. Just my view. That's why Im suggesting if in the future thay do consider changing this, they can do so effectively by implementing a PVP based system status (i.e. Lawless systems) with greater rewards. That way players who does not want PVP can ignore those systems while those bold enough looking for better rewards (trade and mining multiplier increase) can risk go inside a PVP lawless where piracy gameplay and bounty hunting may happen.
ex. You want to do trading with higher rewards? You have to decide if the trade route you take goes through a Lawless PVP system (fewer jumps and higher rewards but riskier) or go though another route with more than 1000 ly more and lower output.
About take the direct route or take the longer detour, that could already be done so it works in game modes, equally well. So everything to make this happen, is already in place in the game, FDev only needs to use it, and tailor the response form the game to fit this new rule set. Like flying through anarchy systems should be much more challenging than flying through high security system for example. As the game do not really care where you are, or what the security rating of the system is, sure the response time of the authority ships is governed by this, and there is no help arriving in anarchy systems, but other than that, you are not really more or less likely to be attacked by a pirate.. but it would make much more sense, that flying an unshielded cargo ship you would fly in high security systems, and mostly avoid anarchy systems. so if the game would add these kind of dynamic adaptation how to respond to player activities, then the route you choose, could matter greatly. and this would fit how other games have different enemy levels on various zones, so if you are just a lowly level 5 and trying to run through that level 25 zone, you would most likely find yourself one shot by just about anything. Now we do not have levels in Elite, but we could treat Anarchy systems as much more challenging places to be, and just as level 5 players learns fast that entering a level 25 zone was a bad idea, Elite Dangerous players would learn that Anarchy systems would be a very different experience. So this would now have no big difference on what game you are in, as the dangerous comes from the security level of the system.
So no need to add the PvP card, the game can just fine create this challenge for the majority of players without having to force them to accept unwanted PvP.
Now, we can expand on this, just as anarchy systems are more dangerous, once you have learned how to deal with that, you can now consider a criminal career, and take new anarchy missions that will have you go to medium and high security systems and do unlawful things, like steal stuff, commit murder etc. and we can now scale the security response to these blatant disregard for the laws and scale up the response. creating a new level of challenge for players. and the more criminal activities you do in any given system, the more dangerous it gets, and all of this without involving any unwanted PvP...
so no, PvP is not need for most players to get a challenge, most of this stuff should already be in the game, FDev just need to use allow the game to respond to what the player does and where the player do it.