Interesting and this has caused the thought that Moodle could do something similar but by using a hybrid of the new logo upload and css settings pre-processing facility. Such that the compiled css would be requested like the logo and if it was not there be compiled server side, sent to the client and cached. Then things like 'Purge all caches' / 'Purge theme cache' event in settings.php would cause it to be reset. This would also provide the capability to have a 'custom less' rather than 'custom css' settings box which would automatically trigger a theme cache purge when it changes - just like it can at the moment.
This would also mean that we would not have to store 'moodle.css' etc in GitHub and recompile it for tracker issues. You could then in theory have a 'file upload' for replacement 'variables.less' and 'bootswatch.less' files.