I think all useless materials should go, and dated things should be unable to be made...BUT, that all currently existing dated items should remain in the game. Some of my favorite gear is 'dated', and a lot of my low level gear is dated. I paid plenty of gil for a lot of my dated items, and I've got a bunch of dated stuff that I sell to people looking to make it into materia.

With dated items no longer craftable, and being materia convertible, dated items will slowly phase themselves out of the game without them needed to be removed from the start of 2.0.