[development] Fixing themes and regions

[Nedjo Rogers]

The region handling we introduced for 4.7 (and that I mostly wrote) is a 
step forward but produced confusion and instability in multi-theme sites. 
It's cumbersome to have to configure things like enabled status separately 
for each theme. As a 4.7 workaround I wrote a helper module, 
http://drupal.org/project/issues/blockregion.

I know that there's work ongoing to improve theme handling of regions. But 
I'm behind on the status of this work. Is any of it for 4.8/5.0?

If not, I'd like to consider the following approach:

1. Drop the ability for each theme to define more than the region of a 
block.
2. Pull the theme-block configuration into a separate table, e.g., 
block_theme, with fields
module, delta, theme, region
3. Limit the UI configuration to region only for non-default themes.

Is this needed/a good idea?