My opinion is that they should use premium materials all around in some models
In all fairness, the main counter to using an all metal body is the wireless charging. Well I don't see it as being as important as most do. Yeah, it's cool and all, but all in all it's really just not that useful unless you're lazy to no end and you can't be bothered with something as simple as pulling out the cable from the phone.
On the other hand, people do like for their phones to look good. Hell, if the One was available on my country right now and I had the money I'd pull the trigger in no time even though I hate big screens with a passion. And this has been a problem with Windows Phones ever since the Titan, Lumia 900 and others. They're bulky, thick and with big bezels. The only reasonably sized WP I've seen until now was the 925 and I believe it could be even smaller if it had an all metal body.
I'm not saying to ditch the wireless charging forever, but it's a sacrifice that should be made in some models. If you don't believe me, let me ask you why do you think so many people with no knowledge of technology go for the iPhone when they could spend much less on a mid-end Android or WP and be well served? It's not always about the apps or being iSheep. They buy it because it looks good (or at least it used to, now it's just fugly), because no matter how you hate it, it feels good to hold. Hell, I'm not a particular fan and I love to hold any iPhone after the 3Gs. It just feels balanced. Now, I love my 820 to bits, but when I hold it, it doesn't feel like that. It feels like it's too big for what it is. Even reviewers said it...
So, yeah... Yes to metal.