We currently need npm for lessc, as part of django-compressor, to compile LESS. We want to reduce the dependencies as much as possible, so we're looking into converting to SASS / SCSS, which has a pure-Python compiler, or simply shipping the compiled CSS / JS files for people who don't need to change them.

Thanks for the congrats!

SASS or one of its variants (SCSS, Bourbon, Compass) would be lovely!

Can we use our own frontend stacks to design the frontend?

Yes, absolutely! Our first principle for Wagtail is that it should in no way impede design decisions.

LESS is (currently) used for the admin UI, and the compiler / compressor is available to the front-end if you want it, but you can easily plug in your own compilers or use plain CSS if you prefer.