This has to do with the introduction of microtransactions.
With Destiny getting microtransactions (as if that game needed any more consumer unfriendly and potentially exploitative practices), it appears as though its entire model of distribution and revenue generation might be heading for a change. Kotaku is reporting that, according to its sources, Destiny is headed towards a future of free expansions and updates, with microtransactions generating the bulk of revenue for Bungie and Activision.
What this means is that smaller expansion like The Dark Below or House of Wolves will no longer be a thing- Bungie will release new quests, modes, and strikes, alongside periodic increases in the level cap, for free for everyone. Paid expansions will be relegated to the bigger releases, like The Taken King this year- but they may, in turn, be priced as high as $60.
I think this model could be better – the ‘expansions’ like The Dark Below and House of Wolves were complete and total ripoffs after all – but I think this will, in the end, depend more on the execution of this idea, rather than the idea itself.