I think that the tablet style GUI will never go away. While Win 10 goes in the right direction, it is moving too slow: they are liars and the reason is definitely not technical. Win10 is not enough for me: still bloated with tablet style GUIware. How many windows versions in order to achieve the Win7 GUI? People need to get used with the fact that the Win7 GUI is dead because MS is arrogant, ignorant and hypocrite.
My "gun to the head" is this:
http://www.classicshell.net/. It is highly stable. Just fire it up, fully disable "active corners" and "check for updates on shutdown" and you're good to go.

Don't worry. Support for Win10 will probably arrive in time.
Relax; it's a preview. I have a feeling full screen apps will not be around by default anymore on the desktop side of things, by the time it launches. There are many months to go.
8.1 is a fair bit faster I just can't stand the interface. I'll move to Win10 if it really does become a proper desktop OS unlike 8.1.
But I don't see any technical reason why MS can't bring DX12 to Windows 7, using a "gun to the head" tactic has not worked in the past see Vista as an example.
Vista could not support DX9 because of massive driver overhauls in the form of WDM 1.0, that greatly benefited end users (after the BSODs were worked out...). Very rarely do driver hangs require a restart, whereas in XP and prior, the oh-so-frequent "driver stopped functioning and was recovered" was a far too common occurence (relatively speaking, not in absolute terms).
I'm sure Microsoft could have retrofitted XP to support DX9, but the validation involved would have been very costly, all to support something that actually would remove the opportunity for millions of sales. In addition, AMD, and Nvidia in particular, had a rough time with crashes on Vista during the early days, and that leaking over to XP would have brought lots of headaches.
On the other hand, DX9 is still around... The reprecussions of that move are still felt today. A few of the games I've played in the past year are unforunately still on DirectX 9... With one of them launching as early as a year ago. And it suffers from performance issues... Wonder why? I wish the guys over at Grinding Gear Games luck for finding more guys to work on their game engine.
Unfortunately today, OpenGL is not a viable alternative. Apparently developers got burned pretty bad in the OpenGL 3.0 fiasco. Also, it lacks in features and performance from what I understand, and porting code over, as well as building the expertise to do so, is costly. When you're faced with eating regressions, it is understandably difficult to justify porting to. Its market share is low for a good reason. "Next gen" OpenGL sounds promising, but we'll have to wait and see.
As far as Windows 10 itself goes, I do not feel like Windows 7's lack of DX12 is like having a gun to my head. I much enjoyed Windows 8, and 8.1. The benefits outweighed the negatives, which were easily managed. After being on Windows 10 TP for a month or however long, I feel like others will be very happy with it. The are some kinks to work out, but so far it is very stable, and the start menu functions better than Windows 7's does, honestly. There really isn't a good reason in my mind to not pick it up, while it is available for a steep discount after it launches.