Here are the two formations that have me drooling.
Dante or Sanguinor
2-5 sanguinary guards units
Special rules :
No reserve roll you choose the turn they arrive and everybody arrive in DS
They can charge the turn they DS but count as disordered charge
Archangels orbital intervention force
3 termi squads of any sort
Special rules :
MUST be kept in DS reserve
one single reserve roll
The termi may either shoot twice (not necessarily at the same target) OR charge the turn they DS but this will count as disordered charge
The first one is all assault units with power weapons that can choose when they come in and the assault that turn. All of my tyranids (ok maybe not biovores) a shaking their claws at GW. The ability to get into assault the turn you arrive is just broken. If I am not mistaken they also have a 2+ save. They also get to choose when they come in so I would assume turn one is an option.
This is just an awesome formation. I would assume that it is quite expensive in points. It will definitely be hard to counter. Maybe if they assault a unit and are left out in the open, They could be brought down in the next shooting phase. It is still hard to counter that many 2+ saves.
The second formation is also awesome. Just think thunder, hammer and shield termies coming in from deep strike and then assaulting. If you want, you can have some shooty ones as well. I don't know marines so I would assume one special gun and/or maybe one heavy gun per squad. I know if given a choice I will go assault Terminators all day long.
I am kind of glad that I don't play Blood Angels. I know I would want to play these formations but I think they are too powerful. I know that they are needed in the current competitive meta. It was better when maybe one or two units could assault from deepstrike.
Thinking of a counter for this is tough. The first hard counter would be a flyer heavy list the five tyrants probably could hold their own against a list like this. Another one might be a dark angel list in the formation that allows overwatch at full ballistic skill. If you can get units with a lot of AP2 weapons you might be able to take them out before they get to you. I think that a knight army will crumble before all those thunder hammers. If eldar keep their bikes in small groups then scatter bikes might work. Unfortunately none of there are options for my armies. ouch!
I am unsure of the costs of units but even if each unit was 300pts you could do a golden host formation with 4 units of guards at 1500pt games. You probably could run one Golden Host and Archangels force as well.
I do believe this will bring the assault phase back. At least for these formations.