Thanks for making Repaint. It looks awesome and I agree with some of the comments here. I'd go absolutely bananas for a convenient web design tool that enabled me as a developer to provide my own transformer.
I'd love to see you make the internal document / node tree you are using into something that is presented to the user and could be parsed into any frontend framework that uses a tree to represent UI. If you created a standard for your underlying data structures and exported/imported the data format defined in the standard. Developers could build to the standard and then write parsers that parsed from and to your data format. So I could use Repaint at any point in my development process and use the transformer someone built to move my design into and out of Repaint and from and into my code.
If you were to create a standard that allowed developers to build their own transformers you would be making a different product then Figma. Since Figma has a better UI and design tool, and you aren't going to catch up. Figma also is already on their way to doing a HTML/CSS mapping, (see their semi-new developer feature)
If you emphasized the open standards approach and built your tooling around leveraging developers you'd have something much more close to a UI platform as opposed to "another website builder". De-emphasize designers, emphasize developers, be the Microsoft of UI building tools.