[...] they are trying to create an import-export SH3D format, but they are requesting for help.

I would suggest to look at the DTD of Sweet Home 3D at http://www.sweethome3d.com/SweetHome3D.dtd or in HomeXMLHandler Javadoc.
The file format is quite simple: a SH3D file is a zip file containing a [font=courier new]Home.xml[/font] entry respecting that DTD and entries for images and 3D models referenced by [font=courier new]icon[/font], [font=courier new]planIcon[/font], [font=courier new]model[/font] and [font=courier new]image[/font] attributes. The data structure is quite similar to IFC as far as I remember.

why finish a html5 export instead IFC import export plugin?

Even if it's a big task, I prefer to finish HTML5 support for Sweet Home 3D because applets for its Online version and Viewer are dying from the lack of support of the Java plugin in browsers and they need a replacing solution.
Support for IFC is a new feature so, as long as it isn't published, maintaining it isn't required yet. Keep also in mind that Sweet Home 3D is a program for a general audience, therefore supporting IFC in Sweet Home 3D is probably not the first thing expected by this public.

If you have some IFC files you can share, please send them to me or share them wherever you want.