New UI’s make you work more, cause you have to spend time getting used to it. In the rare case that a new UI actually improves the usability, that’s great, but as BlackRang just wrote, often thats not the case and pretty UI != productive UI. Besides… one thing that looks pretty to you, might look horrible to another.
Don’t tell me a craftsman wants to paint his tools every once in a while with a new Color. Perhaps Change your room?
Want optional theming for the Editor? Fine by me, but looking at all the broken and missing tools I’d rather see the time spent fixing than giving the broken Saw a new paint.