A few years ago, I worked on IFC format support for Sweet Home 3D with the help of another developer, but the plug-in still needs some refinements before being published. It's not so motivating because there aren't so often requests about this feature.

I just have a question, why finish a html5 export instead IFC import export plugin? Is html5 easier or superior to IFC?

My feeling is IFC / BIM world doesn't seem to match the target of Sweet Home 3D...

You might check old autodesk dragonfly, revit formit or sketchup files for inspiration, sh3d is considerated a predesign program and that mean that already can be considerate as part of a bim workflow