My opinion, and I know I'll get slaughtered for this one, is that the band (including Waters) feel they still have some kind of untreaded ground to cover...or sky if you prefer...and with last year's Live8 reunion concert being such an "impossible" event, they may still have something in the WORKS for their dear fans...
I think it's the only way they may ever decide to record music or tour together again--if Waters IS involved. The three-man Floyd is history.