From Boston's perspective, to get Lillard and Simmons for Tatum, Horford, Langford, and a 1st isn't horrible. I don't think we would (or should) trade Tatum unless he started a "I want out" type of thing but an interesting idea.
For Philly, to get McCollum, Langford, and a 1st for Simmons is probably less than they think they can get but more than they actually will get. If I am Philly, I would take this deal (but they probably wouldn't).
The problem is Portland. Tatum and Horford for McCollum and Lillard is probably not a good deal for them. You are blowing up a fairly good team for a really good young player (Tatum) but one that probably doesn't want to be there. They would be worse in the short term even if better in the long term (assuming they can keep Tatum). I just don't see them doing this.
Fun idea to kick around, reasonably fair on value. Maybe we see the Simmons- McCollum part of this but not the Tatum - Lillard part.