I would suggest - release early!
It doesn't need to be too involved in the beginning. What I would suggest:
- one-paragraph summary of what IBSI is (and what it is not, perhaps!)
- pointers to the paper, phantoms, implementations that comply with IBSI
- pointer to a "live" version of the IBSI document so that people know how to get involved (I recall you were considering ReadTheDocs for that purpose?)
- pointer to the mailing group
Once the site/ReadTheDocs are live, it will be easier to engage people for feedback and participation. I would be happy to help spread the word!