Quote from BagstoneBlizzard will not nerf items. And they will not touch items that you already own. If they change specific items, they might introduce "legacy" as for the old sets. They will just buff everything else.
I used to have gloves with 20% Attack Speed. I think that's enough to prove the precedent.
If they introduce a whole slew of new items that are as good or better than (or let you improve) existing items, this would have the effect of devaluing existing gear.
As I think about this I just try to view what the game would be like if the changes I suggested were implemented. I'm not thinking about the shitstorm of complaining they would create. As I'm fairly certain this will never come to pass I can comfortably theorize on this from a totally objective viewpoint. Sadly, Blizzard doesn't have this luxury.