Think it be awesome idea to add something similar to seasonal bosses, special villains you could have chance of encountering even if on void crusade or just mission in general. That could be slightly tougher than regular bosses that would drop unique loot you wouldn't get from regular chests or crate. Similar to how seasonal chest work to non seasonal game, where you'd have something to be excited about when encountering them and be hopeful for what special loot might drop.

Think more chance encounters with possibility of special exclusive loot would make mission and doing maps more exciting, since you'd always have some unknown probability of coming across something truly or special you otherwise wouldn't. Maybe even create some incitement to try hunt for special drops that make be a thing on its own.