Just going over the leaked ruleset for 5th ed.
It seems like DA players now HAVE to take Sammael if they intend to use the Deathwing assault rules.
Scouts no longer get to set up in addition to your regular mission allowance. In one of the three basic missions you can only set up 1 hq and 2 troops choices. (Dawn of War I believe). Since Ravenwing are FA slots unless you take Sammael then theres the chance that they'll arrive after the Deathwing using the reserves rules.
Thanks GW. You've screwed me again.

P.s. Dont ask for the ruleset. Forum rules say I cant tell you where to find it, but it is out there where anyone can get it if they try.