> What would it take to make an SSG appeal to a broader set of users?
I don't think the SSG, as they largely exist today, will ever gain widespread usage by mainstream users.
But one thing that could drive greater adoption would be to develop an aesthetically pleasing web front-end that lets users write content using familiar WYSIWYG tools, but save the content to local files instead of a database. From there, the process would be largely the same as it is now: transform this directory of lightly marked up plain text files into raw HTML.
So, to answer your question: Make it more like Wordpress.
There is no doubt that SSGs will "grow up" and appear to gain features like Wordpress. The difference will be that SSGs are born out of loosely coupled tools in a toolchain ecosystem. Over time, I believe the successful SSGs will have a decidedly Unix flavor to them. Take http://www.metalsmith.io/ as an example.
I think the future of "SSGs" is that they're going to end up as programs running on the server that watch data from various feeds - databases, RSS feeds, APIs - and generate output from those. Basically, a streaming processor framework. The output would likely be in a "semi-baked" format so that they can contain processing instructions that are executed at request time, or otherwise lazily.
These won't be static site generators any more, and will lose out on the "you can throw it up on Github Pages" benefit, but they'll be far more powerful, and it'll be easier to develop dynamic, data-driven websites.
I don't think the SSG, as they largely exist today, will ever gain widespread usage by mainstream users.
But one thing that could drive greater adoption would be to develop an aesthetically pleasing web front-end that lets users write content using familiar WYSIWYG tools, but save the content to local files instead of a database. From there, the process would be largely the same as it is now: transform this directory of lightly marked up plain text files into raw HTML.
So, to answer your question: Make it more like Wordpress.