If you are going to sell, you always sell high.
Waiting to see how things "shake out" generally will get you nothing in return, because if they perform well, you generally don't want to trade them anyway.
"IF" a player like Soler is someone that you contemplate moving, you move him at his peak. His value declines substantially (see Castro) if you wait until next year and then he regresses. GM's will have his post season numbers fresh in their minds.
You deal on another teams perception of some player, and you hope that lets say, San Diego or Atlanta, would give up Tyson Ross or Julio Teheran for Jorge Soler if that were the case.
It's the chance you risk. You may win, and you may lose.
If I landed Heyward, I would trade away Soler right now (if it could be done) to get one of the aforementioned pitchers that are no less than a #3, with very good potential to be a cost controlled top of the rotation pitcher. The staff needs to get younger in areas.
Heyward would cost the same as a front line starter like Zimmermann, and basically I could get the same type of pitcher for Soler, and improve my speed and defense at the same time.
Probably no one would see it coming via "smoke and mirrors", because they would be thinking that the Cubs are targeting Heyward for CF.
Even if they decided to put Heyward in CF, they could essentially stick Bryant in RF too if they decide to go this route.
The options are endless