The ZIP file generated by Export to HTML5 plug-in contains a second ZIP file named from your project and this second file is actually a simplified Sweet Home 3D file. If you change its [font=courier new].zip[/font] extension by [font=courier new].sh3d[/font], you'll be able to open it with Sweet Home 3D or import it in Sweet Home 3D Online, but only if it's still smaller than 20 MB.