I believe that when they say "all equipment will be meldable", they're specifically talking about all new equipment, as in only items introduced in 3.2 and beyond.

Further, the word "all" might be a bit of an oversight. In other places the devs have specified "raid and tomestone gear", which leads me to believe that it's a change only with respect to combat classes, and that DoH/DoL gear will be largely unaffected.

Finally, even if it does turn out to be applicable to crafting gear, and does turn out to be retroactive, they've also said that overmelding won't be allowed on anything but crafted gear, so in most cases the i180 gear would still turn out to be weaker than i170 gear, unless you stuffed it full of Tier V materia.