In the latest (March) issue of 'Gramophone' magazine, there's an indication of a new Salonen/Philharmonia recording of the M9 'forthcoming' from Signum Classics, along with a tantalizing excerpt of the Rondo-Burleske on the cover CD. (Interestingly, there's no mention of this recording at all on Signum's website.) The magazine also features different present-day conductors contributing an essay on each of the Mahler symphonies (with Salonen taking on the 9th).
Russell