I'd like to give my 2 cents on this.
I do not like the proposed design. I know it'd be hard to convince the team otherwise this late, and the poll certainly favor it also. Still, the proposed design looks like something on OSX or iOS, not Windows. It's a chrome design language, which does not fitted with the rest of Windows UI. I would not proclaim that I'd stop using FDM or anything like that since I like this program too much. I tried something else a couple times but the features always bring me back. However, if the new design get released, I'll certainly start my hunt for a replacement for FDM, or just use the old one.
My suggestion (order by personal preference) are:
1. Go Metro. This is very hard, I understand. I don't mean doing WinRT development (though that would be nice). I mean something like http://www.metrotwit.com/
. Clean, Modern, Simple, but still offer all the functionality. And fit right into Windows 8. You don't even need to do WPF. Look at, for example, the "expand" layout of the current Windows Live Messenger.
Now I'll admit, it can (but does not have to) looks out of place on Desktop as much as chrome design language (i.e. the current proposal), but I prefer it. The thing about Metro design language is it put emphasis on the content, not the UI. In my opinion, the current proposal (and Chrome design in general) is wasting more space on the UI (chrome) but does not improve any content's readability. The only thing it has over the current design is the progress bar, which can be simply add to the current design. This bring to my choice 2.
2. Keep the current design. Maybe a couple re-design of toolbar icon and add the progress bar, but that's all it needs. Current design does not look out of place at all IMO.
3. Go ribbon. Just make sure you fellow the default Windows ribbon and make it collapsible, with user-customizable Quick Access Toolbar (the top left toolbar you see on Windows 8 explorer/MS Office 2007/2010)
2 & 3 are not mutually exclusive. They can certainly be combined.
I must admit I'm feeling down while typing this. I know I probably cannot convince the developers at this point to change your mind, but I really don't like the OSX-ish design. The last one even looks like an iOS app port. If there is no other choice, please at least keep an option to use the old design.
tl;dr version: I really don't like the new proposal. I really don't. It's so important I say it twice.