What could it be?
Update: it’s NOT Liszt.
It could be another Levy Liszt sonata.
koji
As much as I love Levy, that would be a let down. They’re building it up to be something spectacular and I would be disappointed is it was only something like that. Especially if its the live version we already have (thanks to you koji). In any case, I can’t get this volume because I can’t afford to subscribe to ALL their releases. I’m just hoping they find the Hofmann Teatro Colon recital as compensation. 
Brendel’s 4th complete Beethoven sonatas rec 
There’s actually a third Liszt sonata from Levy that was issued on a private LP. Another possibility is an album of live Lewenthal.
koji
I only know Marston issued 3 volumns of Godowsky complete recs, 7 CDs in total.
Inform me plz, what is this Marston Mystery Release? 
June 2007
Mystery Release
52055-2
Our May release may arguably be the most important “find†in the history of recording. It includes some of the earliest known recordings of music; it includes the recordings of artists who have previously remained “silentâ€; and like Hofmann, will change the conception of many artists’ discographies whose output was previously thought to be complete. The sound varies from primitive to clear; the content includes voice, violin, piano, and chamber music; and will contain the first known recordings of many artists and art forms. The TBA title is necessary because this compilation deserves a coordinated publicity campaign and “leaks†may hurt our efforts. This release, as with all of Marston’s issues, will be a limited run. Because of the multi-disciplinary nature of the compilation, only our All Preferred Customers are scheduled to receive this issue automatically so PLEASE sign up to receive your copy including our Vocal and Piano Preferred Customers. We expect this set to be sold out quickly and we want our customers to have the first opportunity to receive this important set.