If i recall correctly, someone did added two handed weapons to all three main classes. Apart from that... i have not seen a mod that gives new set of sprites specific to the Bard and Barbarian. https://www.spriters-resource.com/pc_computer/diablodiablohellfire
It seems the "characters" were prerendered and animated on 3DS Max, then they used some sort of software that rotated in 360 the model and made a sequence of screenshots for the animation used in game.. I think i saw several tools that can do this on the Lurker Lounge forums. https://www.lurkerlounge.com/forums/forum-15.html
You probably will never see this, someone would had to create the 3d Model and animate it in some 3d Modelling tool, then do the sprite animations for each and every action... not that easy, but totally possible to do. If it does happen, it will probably be on the Modders side.
Mostly, i seen reskins/palette swaps of the original characters as "new" characters. Basically the same Characters with different cloth colors.
I guess it would be easier to just take the D2 Barbarian sprite animations and somehow scale them to fit Diablo/Hellfire resolution, so they don't appear Shorter/Taller. I don't know why no one has tried porting the D2 Barbarian to D1.