I didn't read the article so maybe this question was answered there, but why would you only stop using helmets in practice? I say get rid of the altogether.
As I understand it, they feel that helmets do improve safety, so long as players are not tempted to use them as a weapon. Thus, if you remove them from practice, the players will learn to tackle properly and safely, and then, presumably those safer habits learned in practice will be applied in game, even though the helmets are added. Thus, in game you would get the best of both worlds - less dangerous hits, and the safety benefits of the helmets.
That's why I said that for this approach to work, you'd have to start early.