Adding new items exclusively through DLC is an excellent way to splinter the Multiplayer community by requiring all players joining an MP session to have the same DLC installed (otherwise some players have data for the items, and others do not).
While such a requirement is fine for an expansion-sized addition, it did not seem appropriate for a new game mode that was a Kickstarter stretch goal.
There will be new items in 1.0.0.6, and they will also drop in the Crucible.