[kaybe]

This has been discussed before (well, the general configuration for users). The main argument against it was that not having a common experience in the core elements makes it very hard for the community to stay coherent (which is given as desirable) and have good discussions.

Eg when I don't know how you perceive the comments in the vicinity of the discussion, it is harder for me to understand your comment's intentions and finer points.

Of course this doesn't apply to peripherical features such as the colour of the header bar.