Since the last split specialty damage weapon was removed from game / altered (however you want to look at it), I think some of these types of weapons could be added in the game as rare drops.
Rare, because there doesn't exist enough rare drops in this game and split specialty damage was considered too "niche" and "didn't have enough uses". Due to their weaknesses, it should be considered something special to own a split specialty damage weapon.
Could possibly add something like "Antique Argent Peacemaker" as well as "Reforged Sentenza", names can be whatever I don't really mind.
Antique Argent Peacemaker - has the AP's old Elemental + Piercing, but it may or may not retain the new medium damage bonus to undead. I couldn't decide whether to or not to keep.
Reforged Sentenza - Has Sent's old Shadow + Piercing. Same deal with this damage bonus.
The new/old (however you want to look at it) AP has a very low chance to drop from bolt buckets (the things that very rarely have crowns in them) which will now be placed more often in deconstruction zones.
The new/old Sent has a very low chance to drop from smashed graves in graveyards.
And have the old shard bombs drop extremely rarely from minerals.