Support pluggable CSS frameworks

One of the things that the web is moving towards is the use of CSS Frameworks/Preprocessors. There are many out there but the three that continue to pop up are:

• Sass/Compass
• Bootstrap
• Less

It would be interesting to see Fusion take a slightly different tact than a theme such as Zen (which settles on Sass/Compass as its optional framework) and, instead, support a pluggable architecture for whichever framework a developer chooses to use. Out of the box, it probably makes sense for us to support one of them natively by way of example. (e.g. a Fusion Starter Sass sub-theme).

Potential caveats here:

• We probably would not be able to include the libraries by default as they are not GPL (although they all are open-source) so we'd want some "easy" way for developers, possibly through drush, to bring in those libraries. That already exists in drush by way of Libraries so I think we're talking about examples rather than hard implementation.
• To use LESS, it's a Javascript include. To use Sass/Compass it requires a ruby gem installed either locally or on the server.
• A Bootstrap theme exists currently so we'd not want to duplicate function but instead provide an easy way to pull Bootstrap into a Fusion based theme.
• And...

How or if we implement it is left for discussion but I wanted to start some blue-sky thinking on the topic.