@apply should become the new mixin I reckon, combined with native CSS variables. It will take a lot of time (making specs, getting vendors to implement), but it might remove the use for SASS/LESS in a lot of cases.
Does CSS @apply rule solve any real problems? or are we just making CSS harder and harder with complex/unnecessary features??
If @apply works like a SASS/LESS mixin, it does. CSS will evolve and it makes sense to copy the good parts of SASS/LESS and make that native CSS behaviour :)