You have the answer about achievements I was given when I asked about this a while ago, as best as the programmer could remember, not having looked at it in some time.
I did answer why it wasn't feasible.
How many months development time do you think would be involved in redesigning core game mechanics? After such an alteration, there would have to be changes to all quests, etc, and some quests redesigned. Then, especially late in development, there would have to be exhaustive QA done to test everything, because anything could be affected directly or indirectly by fundamental changes to the core mechanics.
That is in addition to the year long development for all the changes that were added to the EE.
