Destiny 2 developer Bungie is implementing a hot fix to the game addressing player complaints regarding the Curse of Osiris expansion locking players out of certain content, which is set to go live along with today's update.

The expansion locked those who didn't own it out of the Prestige Leviathan raid and weekly Prestige Nightfall strike, for example, by raising the power cap. This content was accessible before Curse of The Osiris' release via a lower power cap. As such, the lockout also affected a player's ability to fully complete the game's trophies and achievements, since one includes the need to play a Prestige activity.

In a blog post discussing the matter (click for full details), the studio walks through its reasoning behind the initial idea, as well as what it's going to do in the new update (text from Bungie):

• The Prestige Leviathan Raid will be brought back down to Power 300, and its rewards will drop down to match the new Power Level. All players will regain access to the Prestige Raid.
  • This will allow access to "The Prestige" Achievement/Trophy for all players.
  • This will also allow all players ability to complete the final step for the Legend of Acrius Exotic Shotgun.

• Trials of The Nine will only require Curse of Osiris when it features a Curse of Osiris map. For all other weeks, it will be available to all players.
  • This will allow access to "Lest Ye Be Judged" Achievement/Trophy for all players.
  • Trials of The Nine rewards that launched with Destiny 2 will still be accessible to all players.
  • New Seasonal Rewards that launched with Curse of Osiris, such as the new Seasonal Armor Ornaments, will require ownership of Curse of Osiris to acquire.

• The Prestige Nightfall will remain a pinnacle activity, at the new 330 Power cap.    
  • This means Prestige Nightfall will require ownership of Curse of Osiris.
  • Because of this, we will update "The Prestige" Achievement/Trophy to only reference The Prestige Raid.
  • Moving forward, we are investigating adding a 3rd difficulty to all Prestige activities, so that we can provide both a challenge that stays relevant with each new Expansion, and a Prestige version that is available to all players.

• Normal Nightfall will only require Curse of Osiris when it features a Curse of Osiris map. For all other weeks it will be available to all players.

• Time limited events - Iron Banner, Faction Rally, and The Dawning, will be made available to all players.
  • We will be postponing tomorrow's Faction Rally, to ensure all of our players can access the activity and the appropriate rewards.
  • Iron Banner and Faction Rally rewards that launched with Destiny 2 will still be accessible to all players.
  • New Seasonal Rewards that launch with Curse of Osiris, such as the new Seasonal Armor Ornaments, will require ownership of Curse of Osiris to acquire.

[Source: Bungie] 

Our Take
Bungie clearly misjudged perceptions from players about the importance of keeping content that was part of the base game and graduating its power requirements to only the players who had purchased the expansion. Bungie has a challenging balance to strike here; players with the expansion want challenging weekly content that matches their new power levels, but players without the expansion don't want to miss out on activities that they paid for when they purchased the base game. This latest update walks a middle road, and we'll have to see how the game's community responds. – Matt Miller