Rhy's working on bringing all these features.
Yes, there will be custom content at some point but it will mostly be present on private servers only.
The Official server will surely stay true to the original game just enhanced - stuff like multistory buildings and multiple lot ownership(the former is already in I think).
Think of it like TSO Remastered. Mostly adding stuff that you wouldn't even notice at first just small changes that make the game that much better.
Special CC items during Holidays is something to be expected I guess
If this vision has changed I'm sure Rhy can further elaborate on this subject.