There are contenders for further change - from the many other pre-processors out there to totally new systems.
Flexbox, which has actually been around for a good while now, would allow for much more diversity and malleability in screen layouts. Take up of this has been stunted by lack of browser support, with IE being the usual culprit and continued hold up: http://caniuse.com/#search=flexbox
The next step along this layout path is the CSS Grid, which "is a two-dimensional grid-based layout system that aims to do nothing less than completely change the way we design grid-based user interfaces". Browser support here again lags even further behind so it'll be some time before we can begin to implement these new systems.
Interestingly within the same timeframe of CSS evolution, there is an emerging concept called Houdini, which would in essence remove the need for polyfills and allow developers to render their CSS in all browsers, but again it'll be a while before this comes about.
Crucially all of these developments are only possible when the browser support is there for them. Although it's been a long slog, the double whammy bonus of Microsoft's decision to drop support for Internet Explorer (currently versions below v11 but they've also announced that 11 is the last version, as they put their focus onto the Edge browser), and the overtaking of IE by Chrome as the world's most used browser mean we are closer than ever to use the new tools available to us.