If a player character attacks (or damages) another player character, could something activate which has an effect similar to the "/c hostile all" command? Might be worth considering if this effect only takes effect in instances of direct damage, i.e., damage from AoE effects are ignored.
This would allow the attacked (and any bystander) player character(s) to then react accordingly with any spells/abilities that differentiate between hostile and non-hostile creatures (such as missile storm, Hammer of the Gods, certain bard songs, cleric turning, etc.) without having to deal with the clunky player list which doesn't even do us the service of listing players by alphabetical order.
To minimize confusion on the attacker's end, they can use "/c setally" the command. This also re-emphasizes that managing hostile settings is the responsibility of the attackers and not the defenders.
So, just playing devils advocate here:
This has potential issues with Necormancers / Summoners - for example, Summoner misclicks another player with a cantrip while fighting trolls, suddenly all their fire elementals turn on their own team - or the reverse when someone accidentally clips a summoner with an AOE spell and suddenly everything turns to alpha the offending character.
You could reduce the impact of this by turning it off in quest areas but its still something worth consideration.