What I loved whit Destiny in forsaken was the game mode with I could come back at anytime and progress how much I want to before I had to part ways for work etc etc. What could be a good idea maybe some sort of Tower challenge? A challenge you could do alone or with a fireteam much like the holiday with the hunted forest but without the time limit? You clear a level then fight a boss with mechanics that becomes harder for each level you clear. If you wipe you get push back 1 level or get a penalty like in nightfall and to lose that penalty you have to defeat the boss.