Secondary, so as not to compete with more important primaries.
As an affix, players would be presented with the option to reroll it if it appears on an item.
Tough call: Do you roll off the BoA? Or reroll a primary stat to make the item better?
Also, add ETHEREAL back into the game, also as a possible secondary affix.
For those unfamiliar with how ethereal worked in D2, it raised the overall stats of an item slightly.
Ethereal legendaries (uniques) were always slightly stronger than their normal versions.
Ethereal items used to break permanently when they ran out of durability, however I would propose instead a higher repair cost.