Some information gathered from a sermon by the Superior General of the Priestly Society of Saint Pius X (FSSPX/SSPX), Bishop Bernard Fellay (the French audio file is available at DICI, the FSSPX's news agency), at a Mass after the consecration of an altar in Lausanne, Switzerland, on April 29, 2007:
The Motu Proprio "is a strong wish of Benedict XVI, and it is probable that the text will at last arrive". When? "In May", possibly, but "most probably at the end of the year, or even later".
Fellay also affirms that the Pope would have been sent a letter by all German Bishops which could be summed up as: "We do not want a Motu Proprio".
Source: Le Forum Catholique.