set up the way I personally prefer it.
That's the essence of my dissatisfaction with the current UI: I can't set it up the way I want it. Until I can, it'll feel substandard.
With what they were saying during development back in 06-07 ish, I would find it hard to believe that they did not have modding in mind.
It's a bought-in engine, though, isn't it? I'd guess that the main reasons for not writing your own are the time and expense it takes to create it. If those are major factors, then are you really going to spend time re-writing someone else's engine to patch all that extra functionality into it?