Sometimes you start a new application with LondonTheme.
The during development, someobdoy says, no, better use the DublinTheme,
to swap the theme is easy, but then you are in a horrible mode of swapping layout-webblocks.
This could be made much more easier and friendlier.
This way we can easily test out different themes as well for PoC purposes.
heck even, clone and publsih different version for a/b testing.