Wouldn't it just be better to add replayability through other content than through grinding? Personally I would prefer more activities with random modifiers. Have the 3 story missions you can do weekly have random modifiers. Make public events with random modifiers, or something similar to Court of Oryx or Archons Forge, while this would be rehashing old content it would add variety to what we have. While grinding is a necessary part of this game, it shouldn't be the only the thing to do at end game. I would prefer something with more substance than chasing a carrot on a stick.