Grimiku posted on the official forum some core features announced at the GamesCom Blizzard Press Event during the unveiling of Diablo III: Reaper of Souls are meant to be launched in a patch before Reaper of Souls goes on sale.
It hasn’t been determined exactly how long before the expansion hit stores, but definitely great news for those who prefer to wait before buying the expansion.
We want to implement a lot of the new systems and features in a pre-expansion patch for free. That should include Paragon 2.0, Loot 2.0, Loot Runs, and Nephalem Trials. For now, you’ll need to purchase the expansion to play as the Crusader, explore Act V, unlock the Mystic, and level up to 70. These details may change as development moves along, but we want some of the core gameplay improvements to be available for everyone. — source