Hardware margins are thin, unless you're Apple.
And when I say professional-grade, I mean sturdy, expandable, and hackable to the core. Designed for Linux/*BSD first, that still runs Windows if the end user wants to install it themselves. If something like the Novena can succeed with a 1.2GHz ARM, I'll be damned if something similar with a quadcore x86 wouldn't do a hell of a lot better. It may bring in small change to a Dell of the world, but there has to be _somebody_ in China who would think otherwise.
The way to do it, I think, would be through a crowd-funding type of platform. 3D print a prototype, prove the sales are there, and then you can spend the money on design and tooling for manufacturing.
Every attempt I've seen, though, has either failed, or fallen prey to the lock-in-based lure of Microsoft.
To answer your question, as a picky hardware nut I have yet to see anything worth paying extra for. Give me a 4lb 15" 1080p matte IPS with user-expandable RAM and a PCIe m.2 slot, a SATA drive bay instead of a cdrom, _no_ dedicated graphics card, a non-chiclet keyboard, a high quality trackpad _centered under the space bar_, and a user-replaceable (hot-swappable?) battery that gets 8-10hrs on a single charge and I'll think about forking out extra money. Otherwise eff off, I'm happy with used Thinkpads.
It's a tough crowd to please, to be sure, especially when half of us are perfectly capable and willing to put in the extra effort to get random finicky component X working.