Some very half-baked thoughts; what do others think?
If play is a way of disturbing the rational order of reality (as Stuart cites Deleuze and Guattari, a way of 'plotting lines of flight away from planes of organisation'), and could even be said to be an irrational, or nonsensical form of behaviour, then isn't it wholly incompatible with the project of philosophy, which is all about the imposition of order and the application of rationality?
If we allow philosophy to become an engagement with irrationality (as opposed to a battle against it), then we betray the nature and goals of philosophy.
And if we allow the play instinct to become defined and subsumed by rationalisation (what could be seen as a co-option of play to powers of order and control) then the very essence of play is lost.
How can this be resolved?