My ideal world boss in PvP games is one that you can take down by just zerging it. It doesn't do much damage or have goofy mechanics but has enough HP that a good size raid will take a bit of time to kill it. But when you engage it, some notification pops up world wide to indicate that it's being attacked. And the HP of it will be high enough that an opponent, if they are coordinated, would be able to travel to the boss site and engage you before you can kill it. But because the boss doesn't do much damage it's possible to fight off the enemy raid while still fighting the boss (though it'd be a huge disadvantage still).
I, too, wish they'd just turned on PvP in open world GW2 and forgotten all the separate battlegrounds/match/maps bullshit.
My ideal is similar to yours (but maybe without the world notification of anything). I think PvE for the sake of typical gear/exp gain to get more powerful in PvP is a bad model in many types of PvP systems. But I also value the PvE world as a measure for winning and losing, and a way to introduce risk and reward, etc. So, make PvE have PvP implications (beyond 'gearing up' for PvP separately).
It has never seemed that difficult to me to merge both PvE and PvP in a way that makes more sense than the lame mechanic of simply having NPCs fight for your side. If your guild/group/faction is trying to lock down irondick mine, they can spend resources/cash/points/whatever to add a boost to mining by summoning some big ass orc slave with a hammer that can be killed, or captured and escorted to a rival area by your enemies.
Now, it's not just PvE, but has turned into a fight with PvP implications. Yeah, you're fighting over an NPC, but that NPC and the associated PvE has become a strategic resource for PvP to be won or lost.
Hell, even limit it to a set number of world champions that provide boosts boons, and then let people fight to control them. Or let a group decide to kill it if they feel that's the best decision, encouraging people to team up against a larger force who they know can control the champion, so a one-time assassination mission is formed.
Beyond that, mobs shouldn't be much more than background unless you're clearing them out of an area to set up camp (as a measure to control simply having one player lock down a resource or area).