The Woj rumor scenario is exactly what I have been trying to describe. By playing nice and getting a pick or something, the Nets allow us to essentially trade Irving for Walker instead of signing Walker with cap space. In order to sign Walker for cap space, we would have had to renounce Horford, Morris, and Rozier in order to create the needed cap space. These guys would be gone with no option for us to get anything for them.
With this trade, we keep our "hold" on all all these players. With the holds in place, we can sign the players, sign and trade the players (as we would be doing with Rozier as part of the base trade), or just let them walk.
In terms of Al Horford, I would not be surprised if this was about trading him to Houston but we now retain the option to sign him and keep him if we want. Same for Morris and other lesser players. But this all starts with Brooklyn being willing to do the sign and trade and help out Boston and Charlotte. We will likely give them a pick and Charlotte may give them something too (they benefit by getting a trade exception and Rozier for Walker instead of nothing if this doesn't work out with Brooklyn).