We've just added a new option in your profile settings that will allow you to opt into seeing beta features which we are testing out on the site.
At the moment this will just let you see our working version of post previews which will be a button that shows up next to the save draft button.
The features will be works in progress, but you'll see them before anyone else - for better or worse. For instance, there's a really weird css bug on osx safari that prevents either the draft button or preview button from showing up (God bless front end development.)
And for any developer or developer-curious hubskiers our there, the markdown renderer we're using is based on markdown-it and is open source. As we find bugs and discrepancies between our sever rendered markdown and the preview rendered markdown we'll be updating that repo with bug fixes and tests. Eventually we'll be expanding the features of our markdown as we move away from arc to languages with more developer support.
Nothing at the moment, unfortunately. As we continue to develop we hope to open source more of hubski and its tools so people can help work on it. For now it's just this, which mostly some extensions of a compiler. We'll definitely keep the community informed with the #devski tag though.