Why bother if you'll eventually turn human or youkai and gain skills to compensate this loss?Try to work around it...IMO it's logical that hanyous should be unable to gather enough jaki to be able to channel into hitting several opponents (watch the anime...hanyous don't have much jaki)...
Instead of working on such a skill i think a better use of time would be working out the bugs with the present skills such as stats relating to the dmg they make (i know it's in the works,it's just an observation)
Instead of giving hanyous a skill to attack all mobs in a room maybe we could have levels in elemental skills (for the future upgrade of the elemental system)...For instance we could have something like Terra crush for the first level of your chief elemental skills followed by a stronger skill (let's say Fissure ...just a name that came to mind...)that's stronger in dmg or effects and lastly Earthquake (another name to fit the subject) that marks the mastery of the elemental class you have,this last skill could have an attack to affect all mobs in a room.
Of course you can give elements different skills in range,power and effect,thus enhancing the concept of elements further,giving them a more active role in the mud...
For instance wind could have a trip like effect (knocking the opponent off balance)...Ice a freeze (stun) effect,fire a DOT(damage over time...WoW players know what i'm talking about

),earth a slow effect or things like that...the possibilities are quite numerous in this regard...Of course it's the builder's call on whether or not to do it,and this is just something i'm making up as i go...but IMO i think it'd be a cool addition to the mud...
My 2 cents on the matter at least...
Kagomaru