I think that the Wit that has appeared in the last few chapters is an imposter. He seemed to be referencing Preservation when he was talking about Shards who’s vessel had died but he mentioned that “we didn’t realize it at the time” which I think is weird since I suspect Wit would know about the mists being preservation. In this chapter he mentioned witnessing a mortal give up a shards power, which seems to be referencing Vin at the Well. But the way it was worded was almost exactly like a line from secret history. “… She did the most selfless thing he had ever seen” which is when Kelsier watches her give it up and release Ruin.
This Wit also disappeared between the meeting of the monarchs and the meeting where Dalinar talks about Cultivation talking to him. He also threw a bowl and hit Lift which his Torment should prevent and I don’t think not seeing her would get around his Torment, because then he could just get around it by closing his eyes. He also sat backwards in a chair just like Kelsier.
In the prologue we see Galivar remark that Thaidakar was doing something that looked like light weaving and in an earlier chapter with Shallan we learn that light weaving can be substantiated to interact with the physical world like real objects. We also see this in Yumi with Design having a light weaved physical form. I propose that this fake Wit is actually Kelsier using a substantiated light weaving to push Dalinar into going to the Spiritual Realm, maybe to find BAM or for some other reason that we don’t know of yet. We will have to see what happens when Dalinar is sent into “Wit’s Memory”.