The DOOM Arena - Slaughter 5 Random Boss on really high difficulty (GR 65 base).
Shadow Run - Kill your evil Nephalem soul running all over acts, this soul is fast try to kill it before the end of her run !
Crush the Map - Crush a one opened map (same GR difficulty settings mechanic). This time you got same amount of progression worth mobs in the map. you have to miss zero mobs to finish the challenge, no boss at the end, BE FAST ! ( i had this mode idea because i were pissed off corridors and cave. )
Daily Events - Bounties, same as those we know atm, you got many more materials from doing it, cause you can only do it one time per day, event get refreshed every-night at 01-00 AM, Keepo
Tourment 20 Difficulty - Meant to be designed for rifts only, you win same amount of xp / loot than T10 but Bosses drops 10 GR keys and drop even more stuff, bloodshard and materials, Care this is a hard mode, will make you feel to be back in Armageddon Vanilla Act 2 !
Some few ideas i had in my mind