Though I am new, I have followed this forum since before HoA, delighted with the theories and speculation on the metallic arts. I have since become enthralled with Hoid and Adonalsium so I'll jump right in...
I am currently doing a thorough read through of WoA, searching for the elusive Hoid reference. I'm nearing the end, but have had a change in idea before even finishing. Up to this point I have been marking anyone alluded to with an "odd" quality or behavior. I have disregarded any other qualities (including gender or age) due to the statement that he is "heavily in disguise". Nevertheless this may not refer to his appearance, so I added anyone who was bald or short (Final Empire description). A few of these have been mentioned and rightfully dismissed.
On pg.42 Teur is referenced as having, "...natural desire for notoriety would make him want to gossip about his experience." And a couple paragraphs later, "Teur apparently had a reputation for tall tales." If it wasn't for him being named I would lean toward a Hoid reference.
pg.44 young man with club leg surviving as a skaa plantation worker
pg.46 the man with the guards (never referred to directly as a nobleman, but Vin was referring to them at the time)
pg.47 the bald man following Vin (though he has hair on the sides of his head)
pg.49 wolfhound merchant
pg.72 bob of light; unfortunate late night traveler (dismissed, added because Vin doesn't dwell on it)
pg.78 dark form in the shadows (dismissed, likely tensoon/Zane)
pg.87 obligators in back showing no reaction to the comments on them (Vin worried about the strangeness)
~pg226 dressmaker/assistant, who knows of fashion outside Luthadel, knows Vin (dismissed)
pg.229 bald man with cap (dismissed)
I went a few hundred pages further, but I stopped because this didn't seem to be getting me anywhere.
Mr. Sanderson said that most of Hoid's influence had to be cut from the book, leaving only a small hint. And that we should be wondering what he's been up to in these books, so I thought to start reasoning differently.
Hoid might not be referenced to as a person at all. It may just be his influence that sparks something odd noticeable in another person. I think that Cett is the key. He led Vin to the "man humming to himself" out in Fadrex city. Which means that he had to have contact with Hoid before he left for the Luthadel seige in WoA.
On pg. 394 Cett is seen by Elend as having intentionally put himself in a, "no going back" situation because he's desperate. Maybe he came to Luthadel only because of the influence of someone (Hoid) back in Fadrex. (Though this doesn't make much sense because the influence would have had to happen before WoA, and he tells Vin later that he figured Straff would come for him eventually and he had no allomancers)
Ham is of course noted many times for his strange behavior, not as argumentative or philosophical as he was before
On pg.306 Demoux is seen as walking stooped and nervous, later (336-341) when he meets with the church members and Vin asks him where he first heard about her bringing back the sun and stopping the ash falling he doesn't know, Vin chalks it up to rumors and doesn't mention it again, could Hoid have started these rumors
At the end when Elend is stabbed and dying, Vin finds it eerie that as he grew closer to death, he actually seemed more in control...and then he tries to say something.
I think, from the way the deleted scenes footprint (assuming it wasn't marsh, like the final version footprint at kredik shaw earlier in the book) is mentioned by Mr. Sanderson, it is most likely from Hoid. Since in the deleted version the footprint was next to the fired clay with a metal sphere at the center (which seems an awful lot like a planet to me) maybe it was Hoid that put the unused one there and TLR never saved one at all.
Overall I think Hoid was trying to help, and not necessarily Vin or the group, although that is very possible. He might have just been trying to help the planet, or Leras and Ati. Seeing as he is himself bonded with a shard, he might see his responsibility/power (planet hopping) is to help/unite other shards.
Boy, that's a jumbled mess isn't it. Just throwing things out there b/c I'm thoroughly obsessed with Hoid and Adonalsium and haven't read any new assumptions in a while.