Okay, so this is like 2 posts rolled into one. Part 1- How will other "Elite" armies do in a post GK meta-game. Part 2- Thoughts on how Blood Angels will combat this new threat.
Part One-
So what I fear most of this upcoming book is that it will be an army of super elite warriors that armies of elite warriors/assault armies won't be able to handle. Take things like Blood Angels (especially DoA), SW Wolf Guard/Thunderwolf, DA Death Wing, CSM Khornate. These are elite (assault) armies. Numbers around 40. What I am worried is that an army of 40 of them will not be able to handle an Army of 30 GK. They all have Power Weapons and Stormbolters, plus stat boosting weapons and powers, so they can outshoot and out kill a straight up DoA army, as well as many other power armour armies, and it won't really have the numbers to deal with it.
What is the scariest part of the GK is the Grandmaster ability to make d3 units scoring. So you can take mimimum Troops and still be confident that you will have 3-5 scoring units, more if you combat squad. Then you can have personal teleporters to make these squads zoom 30 inches to cap/contest last turn, including beastly montrous creatures. AND you know you have very few Kill Points to give up as well, since you are as small as small can be. Where as other elite armies will likely have more kill points and need to take more Troop choices to cap objectives.
The name of the game against the GK will be volume of fire/numbers. So horde armies are safe there. BUT Elite armeis can achieve this too. We will have to localize our strength and overwhelm/outnumber them in one spot, eliminate, then move to the next. As well, get the charge. ALWAYS. You need to bring the number of attacks that charging can. And you want Furious Charge, as I5 will give you a chance to eliminate some of the power weapons before they hit back. Anything that can help here too will be critical. Lighting Claws, Litatnies of Hate, Chapter Banners, etc. etc.
Part 2- Thoughts for BA
I think there might be a slight paradigm shift in BA. Almost everyone and their mom will include an assassin, the Vindicare being the most likely candidate. This puts out priests in great danger. As well, everyone carries a Power Weapon, so even clever movement and assaulting on your part won't keep a deadly weapon away from a priest. Furthermore, FNP isn't as good against a Power Weapon weilding army. BUT priests give that important Furious Charge as I pointed out above.
BUT there are ways to do this without Priests. Namely Astorath and Death Company.
These guys are FNP, furious charging, able to have power weapons and the like, and Re-roll to hit and wound with Astorath/any Chaplain. Plus higher WS to boot, meaning you are harder to hit.
Astorath also has the advantage of making your normal BA squads FC and Fearless, making up for the loss of a priest or two.
In my opinion, Dante and Mephiston are out. As are Sanguinary Guard. Too expensive and vulnerable/useless against an army of power weapons.
WHAT IS IN is Chaplains, Librarians and Dreadnoughts. Bikes are also a little more valid with their boosted Toughness. But back to the others. Chaplains I already pointed out as beneficial with Litanies of Hate.
Librarians are now CRITICAL. Psychic hoods will really be essential to combat the psyker crazy GK. And BA Librarians have some nice powers to cast on themselves/Blood Angels rather than just on enemies. Quickening will give a needed I boost, The Sanguine Sword/Force Weapons will be great against Dreadknights/Paladins.
Librarian Dreadnoughts and Death Company Dreadnoughts will be great. Especially with Blood Talons. The Librarian ones will be able to use psychic hoods against the GK, plus thier force weapon and/or quickening make them Dreadknight slayers. Armour 13 on the front makes them nigh invulnerable to the average GK, as even Hammer Hand and Might of Titan powers will not be enough to hurt them and you are back to only S doubling weapons being able to. A 12 on DC dreads are not as good, but still good enough to avoid penetrating hits with both those powers on them unless they have S boosting weapons, plus they ignore Shaken and Stunned anyways. The fact they fleet and FC into the GK will be clutch though, as they will kill several a turn with little chance of reprisal back.
Lack of High S weapons/long range make Storm Ravens (Dreads+Ravens) and Land Raiders really good, and TH&SS termies are still a good choice.
As for deployment, just avoid DoA and deploy your Jump Troops on the table or mech up. Too many things in the GK army are deadly/bad for the Deep Strike. You will either get slaughtered when you land or not be able to land at all, so just avoid it. And be prepared to face your own tactics, as they are likely to use DS alot. If they are all DS, you can risk deploying from DS yourself, as you can beat them in with DoA.
In short, we will have to play with units that untill now have been uncommon. You will have to be even more concious of what you are doing with your limited numbers and when and with whom to chage. Ranges for powers, assaults, and psychic hoods will be critical to keep in mind. You will have to earn your victory. You will then deserve it. So let Churchill motivate you and hopefully some of my ideas work to your advantage.