Slatikin did the entire Beethoven/Mahler cycle in D.C. a couple of years back. By this, I mean the Beethoven symphonies with Mahler's retuschen. Unfortunately, nobody recorded it. Although, there must be radio quality tapes of it sitting in some archive somewhere.
The Schumann/Mahler have been done before on the BIS label. I don't think that they got particularly strong reviews, so it'll be good to hear another attempt. Some claim that the Giulini/L.A. Phil. recording of the Schumann "Rhenish" (#3) on DG is the Mahler version. Frankly, I don't detect a big difference. I'm just hoping that Chailly throws in the "Konzertstuck for Four Horns & Orchestra" somewhere along the way - it's my very favorite work by Schumann.
Barry