Well, with the case you pointed out, you could put both offending players on your ignore list and log off. It wouldn't even be considered combat logging as you are not in combat. The tools to deal with that are already in place.Because things like - to pick today's complaint... - https://forums.frontier.co.uk/showthread.php/442716-New-Low-for-the-“Gankers”… wouldn't count as PvP (other than a minor trespass crime vs an NPC at the end, aren't even illegal)
They can't implement a "PvP flag" until they can reliably determine the difference between a PvP action and a non-PvP action, and the difference between the aggressor and target in a PvP action. Both of those once you get past the most obvious cases are incredibly context-dependent, and if Frontier could program an AI that could do that they'd be making trillions from it in real-world applications rather than messing around with computer games. In practice, the only way to guarantee no PvP is to prevent other players from instancing with you ... which Frontier provide in the form of Solo mode (and to an extent in PG, if you settle for "no players you don't trust can instance with you")