+1 this is my most sought after feature.
My ideal world would be some sort of fine line between Webflow and Visual Studio for when I need to build custom solutions (authentication, management, reporting etc) - I think the closest thing to this is being able to import your site back in or allow an external repository to host (ie: GitHub). Exposing APIs to the community could be an interesting experiment and some pretty cool extensions could be cooked up.
To go one step further, I've shown Webflow to a few of my designer colleagues. They absolutely LOVE how fast this tool can prototype saving them hours of time writing boilerplate. Clients could see results super early and with some being very indecisive, they could save us the headache of having gone down the wrong design path - and we could just export the code after sign off and import it into our environment.
This is a gold mine guys...or is it just me?