There are currently no suitable auto attack replacement for dual wield melee witch hunters and Reaper builds.
I would have hoped that the expansion would have added suitable attack replacement for the acid/vit/chaos damage types (and Aether for the necromancer/arcanist melee builds for that matter) in the same vein that the “Shard of Beronath” is now used for elemental builds. Sadly this was not the case. Yes you can still use the shard with other damage types but if feels quite awkward to have a elemental attack as a acid or vit build, not to mention the DPS loss compared to elemental builds.
If for some reason your are against adding auto attack replacement options for these damage types, then please make ABB do damage on both the offhand and the main hand for melee, especially considering the changes to Venomlash. Why add acid conversion to ABB + Acid bonus to a weapon suitable for dual wield when the skill is an actual as DPS loss (or a very small DPS increase with heavy investment) when using it as a damage source instead of just using it to trigger Lethal Assault?
Why would you spend skill points on such a skill as a dual wield melee build beyond the 5 point needed to get 100% weapon damage to get the full amount of flat damage to minimize the DPS loss when triggering Lethal Assault?
Yes you can use shadow strike for dual wield melee builds but this currently the only viable melee dual wield skill, I think these type of builds could use some more options.