I think the Tosun and Bolasie shouts are because they are players Palace have obvious had or been interested in before, so it's understandable that people would use them as leverage in any proposed deal. It's not disrespectful.
Some of the others don't make any sense. Like I've seen shouts of people saying Sigurdsson or Delph or Besic, who I don't see as being a good fit for Palace at all, as they seem fairly packed in that area.
Walcott and Iwobi have been mentioned as they are similar, albeit currently less valuable/impactful versions of the same player, ie, wide attacking players who can carry the ball at pace. But they are also both from London, an added attraction to either player.
Without trying to sound patronising, i think of all players mentioned, Iwobi could actually be a decent shout. He is younger and has a similar profile, but it just hasn't happened for him here. He just doesn't seem like a good fit for us. It happens all the time, including Zaha himself at United. Its not disrespectful to say a player could be of value to another team just because they are the make weight in any deal.
A move back to London, and a fresh start, giving himself a chance to prove people wrong could be exactly what he needs. Especially considering the manager who signed him has left. He may not be in the new managers plans.
If a deal like that were to happen, Palace would of course lose their Star player. But it would be a player who wanted to move, and they would instantly back fill his position in the squad and receive the additional transfer fee on top. Alternatively, they could get a lump sum that every team then knows about, and every target of similar profile players jumps up an extortionate amount, as Sigurdssons value did when we sold Lukaku.
I'm actually surprised player trades don't happen more often than they do. In certain instances, obviously not all, it makes a lot of sense.
P. S. I should say, for the record, i'm not even that convinced of Zaha as a target myself so not advocating the deal, just that I understand it. Im just basing it on the evidence that seems to suggest we have had or maintain an interest and the current value of the player. I also understand the attachment side of things when it's a fan favourite. So any Palace fan reading, believe us when we say we have had it all before. Every team has, barring say, Real Madrid.