Fr Z has picked up a most interesting snippet from Andrea Tornielli: L’ultimatum del Vaticano ai ribelli di Lefebvre: pace se accettate il Concilio and has done us the service of translating it with his own trademark emphases and comments. (Cf. Countdown: accord between Holy See and SSPX)
The upshot is that the SSPX have been asked to send a response to Pope Benedict's proposals before 28 June - that is, the Vatican's close of business for the summer.
Rorate Caeli has further news that the existence of this offer has been confirmed by the SSPX.
I pray that this will indeed be a concrete step to the solution of any remaining canonical difficulties and that we may soon see the SSPX clergy at our deanery meetings ;-)