The latest development (some time ago) in these negotiations, as I understand it, was that SSPX was offered a prelature similar to that of Opus Dei, which would enable it to work in any diocese without the local bishop's permission. Bishop Fellay's response to this was to impose two conditions, which SSPX considers non-negotiable, as I understand it. Firstly, the excommunications imposed on the bishops consecrated by Lefebvre must be lifted and secondly, the Tridentine Mass must be accessable to any priest who wishes to celebrate it at any time.
After the passing of several months, the Vatican has yet to reply to these demands as far as I know.
They were offered an apolstolic administration, even better. Pretty much complete freedom, but they didn't take it.
patent