Basically it's like how DW5 was: Not much improved visually, but there will be new characters, new weapons, a new mode, new gameplay features, true musou returns, and the story will be rewritten from scratch.
They need to add more Shu and Wu characters. Wei keeps getting a ton of new characters. Honestly Jin is an extension of Wei so I count them as Wei characters.
A lot of characters were decloned in WO3 including Cao Cao, Sun Jian, Sima Shi, Sun Quan, Yue Ying (got her scythe back), Guan Suo, Gan Ning and Sima Shi to name a few.