Lately I've been working with designers through Sketch + Zeplin and its been pretty great. I like being able to pull CSS and SVG/PNG assets out of the tool and it speeds up mockup to built site quite a bit.
What worries me about a tool that outputs html + css is then having to take that markup and integrate it with whatever client side framework or server side template engine so that its consistent with the rest of the code base, follows set code and style standards, is fully responsive and adheres to whatever arbitrary standards are set by the dev team.
I just don't have a lot of faith that a tool can be flexible enough to output markup that can then be used effectively. I imagine a developer will need to massage it into place in order to get it to conform well and by that point it might have just been easier for a competent web developer to build it from scratch. For prototyping or building out functional mock ups, it could be quite useful, but if the end goal is to hand a developer some markup and stylesheets and then let them build out the business logic, then things could get messy pretty quickly.
It's a good dream though and I hope that one day we can let designers do more of the view layer work but I'm cautiously optimistic.