I am convinced that 5th edition is real, and that it will be released this year. I do possess a draft of the rules. Overall, I do believe that the game will improve as a result of them. Mostly, they're very well thought-out changes that nerf units that need to be nerfed and boost choices that otherwise are commonly overlooked.
Regarding the DH specifically...
The changes that are (likely) coming are definitely mixed. I believe that I have lots of adjustments to make. Highlights of the rules changes that will affect me the most....
The Infantry "Run" Rule
That just means things can assault my limited numbers of GKs that much faster. I would almost never choose to run, as that utterly wastes the stormbolter dakka.
Mobile Walker Weapon Firing Limitation
The combination of walkers only being able to fire one weapon on the move and the overall increased survivability of tanks is a direct one-two punch to my (our) army's greatest weakness. The traditional GK list relies on as many vanilla GK squads as is possible. backed up by 2-3 hellfire dreads for mobile anti-armour. (And that's always been my core, too, though I've often mixed in non-GK units for fun, variety, and tactical options, most notably Seraphim.) Now I pretty much have no choice but to load up on land raiders to handle my armour duties ... but, of course, each raider costs me an entire squad of GKs. I'm caught between a rock and a hard place.
Fortunately, I just bought and constructed 2 normal raiders and a crusader, and even played my 1st game last night with a pair of them in the list. I managed a solid victory, so ... we'll see.
I have gone back over my lists, and I think that 3 dread lists are still viable, if only because it frees up points for more GK Troops squads (see below). It also means that, for the first time, I feel like TLLC/DCCW dreads should be given equal consideration with TLLC/ML dreads for anti-armour duty. However, the inability to move and fire all weapons puts a serious crimp on armour-hunting with dreadnoughts. This holds true even when I included my usual inferno pistol-toting Seraphim. (Which itself has implications. Again, see below.) I find myself strongly favoring land raiders in a way that I never have before.
Only infantry Troops Are Scoring Units
This rule will have a massive impact on me and I think, all DH players. 5th edition is mostly an objectives-based game now, and VPs only come into play for tie-breaking purposes.
Personally, I think having only infantry Troops as scoring units is a ridiculous rule, impossible to rationalize. But outside of "logic", I do agree (begrudgingly) that, overall, it will be good for the game. However, it's not good for my army. (I don't think it's particularly good for any GK army, actually.) It means it'd be stupid of me to slot GKs for Fast Attack teleport duty. With a new reliance on land raiders, every GK squad must be Troops either taking a ride or hoofing it. I cannot conceive of building any army with fewer than 3 Troops choices, either -- already a chore to achieve under 4th ed! -- which means I can no longer afford a lot of the fun units like inquisitors or assassins. Nor can I use Seraphim any more, either. I can't count the number of games where the girls and Eversor have saved my bacon. They're such great units for pulling off surprise moves or for countering some of the worst threats that face me on the table. They're tactical swiss army knives of the first order. Now ... they're gone.
I've never been a pure GK player before, and I'm not really looking forward to being one out of practical meta-gaming necessity. I was gearing up to try it out anyway, but mostly just for fun. I'm irked when meta-gaming considerations interfere with my list-building. And 5th edition does that in a major way.