Making Marrowrend cleave in aoe would be a nice change, especially since BDK aoe completely sucks when you don't have D&D down. One of the things I found as a big struggle for BDK while playing one for the first time this season was their on-pull aoe threat. You currently need several GCDs to really start generating decent aoe threat (drop D&D , pop blood boil, possibly marrowrend for bone shield, and then start cleaving with HS). This often meant that I could lose threat on 1-2 mobs easily on pull to dps popping large aoe cds (spear of bastion/bladestorm was my absolute nightmare). Coming from playing a VDH main, where getting initial threat on a pack is exceedingly easy (throw a glaive and leap in, pop immo aura, you're good to go), I felt like BDK aoe threat, especially at the start of a pull, is absolutely terrible. Having Marrowrend cleave would make it ideal for generating bone charges on pull, and give a good chunk of aoe threat right when you need it the most.