Blizzard’s said they want more DKs to spec blood or frost. Blizzard’s also said they balance encounters around Replenishment, even in 10-man (please note this means they’re balancing raid encounters around an ability that three [soon four] specs have - that’s three [soon four] out of thirty that will become more-or-less mandatory. Take the player, not the class - yeah right).
So, with that, here’s my idea. I’d put this in the Blood tree, 3 points, on the same row as Spell Deflection - no one takes that anyway, not even lolblood tanks, because there’s not enough directly-targeted spells to justify it.
Blood Spray: Your Blood Strike, Heart Strike, and Obliterate critical strikes cause the target to bleed for X plus X% of weapon damage, and have a 33%/66%/99% chance to grant up to 10 party or raid members mana regeneration equal to 0.25% of their maximum mana per second. Lasts for 15 sec.