I'm glad to see you guys are open about the idea and taking suggestions. I most definitely can offer my input, but it should also be at the discretion of multiple players and ultimately the staff at the end of the day.
If there is going to be an artifact to discourage 1vX, it should need to be used tactically and like many artifacts, have a counter. I think it should stay away from Damage Buffs / Debuffs as the current way of fighting is heavily reliant on outside sources of damage besides a players own Melee / Projectile attacks. I think Regen is unnecessary, because with a full Protection 4 set and two stacks of food, players already will not die from external damage if they space out their Saturation. Fights in this fashion with experienced players always end in armor breaking before actually dying from damage. This being said, I think if there is going to be a 1vX deterrent, a Speed BUFF to the player getting attacked would be the most balanced. As Clo mentioned earlier, the artifact could Proc after say 3 hits from separate players within a 10 second time period. This would apply a small duration speed buff to the target to allow them the extra ability to escape if used right. This means water, which is all too common in 1vX fights, would still be an unsafe option, as players can Pearl / Bamf faster than a 1vX target could Speed Buff + Depth Stride away. However, on land, the speed buff would greatly benefit an escaping player if used in combination with Pearl into Bamf teleports. Keep in mind a buff like this could also tactically be used for chasing if a team purposefully turned off thier Team PvP Protection. An attacker could have their team hit them on purpose to get a speed buff as well for chasing, or various other situations in game. This would also add an interesting dynamic outside of team fights, where teams could speed buff each other for getting places, etc. Typically more than 3 members of a team are not on at a time, so if it took 3+ to activate the ability, it couldn't be used as often for chasing teams unless they had 4+ members online at a time.
That's my input on the subject if it were to come into development, but I'm just one person. I can and will put more time into it if you guys want some player-based ideas for it, but atm I've actually been putting a couple hours of work into a mega-post about Artifacts dealing with Bugs, Balance, and Suggestions. If it's alright, I would include this in there as well so it's more public knowledge than players maybe finding it based off the OP in this thread?