Me, too! I really thought it would be added for private play as well.
I don't like to have the speed and stress of multiplayer games all the time, and I so love Walnut Hills. Want to explore it for myself. I really don't get why it should be difficult to add it for private plays, even if they are not able to cut out the new characters. Isn't it our own responsibilty which characters we chose in our private/solo games? So if someone likes to stomp the grounds with Z-Mechs, let him try. It's a private game, and if that crashes, so what? People know or should know which characters belong to Walnut Hills.
I really thought that after the Portal Event I could chose that new/old world for my own game. It can't be that difficult to add, and why don't let they decide players if they prefer to play solo or private?
Let's hope that we really get this map for our own way of gaming! I'm fed up with the usual maps after all this time.