Here is Rorate Caeli's take:
The extremely well-informed Spanish blogger Francisco José Fernández de la Cigoña (whose blog La Cigüeña de la Torre was, for instance, one of the first to predict the nomination of Cardinal Cañizares Llovera as Prefect of CDW) had hinted on the nature of the "explosive news" since last week - and since November, in fact.
Today, he confirms that his sources report "explosive news" related to the "Lefebvrists" [sic] - probably the removal or withdrawal of the excommunications of the four Bishops of the Priestly Fraternity of Saint Pius X (FSSPX / SSPX), consecrated by Archbishop Marcel Lefebvre and co-consecrated by Bishop Antonio de Castro Mayer in Ecône, Switzerland, on June 30, 1988. Fernández de la Cigoña predicts the Papal act for "tomorrow" (though it is unclear how long it will take for the act to be made public).
(Archbishop Marcel Lefebvre, Bishop Antonio de Castro Mayer and the Four)
This story is gaining further steam. Well respected Vaticanista, Andrea Tornielli is now reporting this story: Il Papa ha firmato la revoca della scomunica ai lefebvriani (The Pope has signed the Revocation of the Lefebvrist Excommunications).
Here is the story he reports in an NLM translation:
The decree will be made public in the coming days with which Benedict XVI has determined to lift the excommunications imposed on the four new bishops ordained by Archbishop Lefebvre in 1988. Back then, in addition to the four (Bernard Fellay, Alfonso de Gallareta, Tissier de Mallerais and Richard Williamson) had also been excommunicated Lefebvre himself and Brazilian Bishop De Castro Mayer who had participated in the ceremony.
Now, with a truly magnanimous gesture, granting the request made by Fellay, Benedict XVI has decided to lift the excommunication. Excommunication that, it should be noted, has always only covered the consecrating bishops (Lefebvre and De Castro Mayer, both long gone) and the four consecrated, but never the Lefebvrist priests nor the faithful.
One note on this story. While it is clear that this rumour applies to the four bishops consecrated, the fate of the consecrators remains an open question mark.