I don't think many of the issues will be a problem.

The Modding Stretch Goals are being done by a separate team.
So there shouldn't be any issue with delays in that sense, and considering GM mode requires a unique tool set - it is probably made by the modding team as well.

So the primary cause of delays would be skills \ romance \ mask \ hall of echos.
Personally I wouldn't mind if the Mask + skills + romance was delayed as a post release update.

After all it would give a reason to play the game again a few months later down the line.
Also allowing the content to be released earlier then later.