Bit late to this party but I've recently switched from using Textmate to Atom and, one of the packages I've installed in Atom is Less-Autocompile, which automatically pre-processes
.less files into their corresponding
.css file. All you need to do is add a couple of lines of comment at the top of the
.less file to tell Less-Autocompile where to output the compiled
.css file and it will automatically generate it, every time you hit save.
I'd be a bit wary of over-burdening Hugo itself with too much 'everything but the kitchen sink' functionality [Although a plugin system might mitigate this a bit].
Anyway, having previously abandoned attempts at working with CSS pre-processors because of the lack of integration with my [then] workflow, I'm pretty impressed with how seamless my newly discovered Atom + Less-Autocompile makes it.
I've written about this and a bunch of other packages I find useful in Atom here:
My Atom Setup
Given that probably 90%+ of the time I spend in Atom is working on my Hugo sites [whether writing posts, hacking templates or building themes], it may be of interest to others of you looking for a near-as-dammit "one stop shop" for your Hugo tinkering.