Where you hear this? I heard the opposite, that they'd confirmed they WOULD continue with metal. Anyway, the build material doesn't affect me, I'd take build quality and function anyway. I mean if they use plastic, it means they could have a lighter phone with higher durability that could also have features such as wireless charging and a removable back. All this is of course even less important when you'll quite likely be covering the metal in a plastic case, as I have.
Having said all this though, I don't think the beautiful design was unnecessary. I'm proud to show off my naked phone and even if it was made out of plastic, it'd still look good. I can understand that to some people though, an "industrial" metal phone is important and sometimes a reason to choose another device such as an iPhone.
Sent from my HTC One