You tie beating the last unimplemented boss into the server transfer function. Like proposing the player leave or remain behind change the keystone to work on multiple people and lead the army of thralls and pets to leave with you but maybe giving you a permanent single bonus point in one stat if you leave but with a negative subtraction in another both of which counting outside of the max so a perm bonus doesn’t take away a potential cost and the negative allowing an extra unspent point. but just 1 point. It would take beating the game over and over again to max out.
Or perhaps you could be granted with a consumable: heart of the conqueror that does either one of these things at random. Or bless/curse the player to have a random negative/positive thrall perk applied to the player for a maximum of 3 perks like the thralls.
PVPer’s could seek this. PVEer’s could seek this. Gives a replay factor to try and max out or get the right combimation of random perks added to the player.
THIS DOESN"T HAVE TO BE A GAME DEVELOPMENT ONLY THING the modding community could consider this, if they aren’t already.