There is no overarching blanket concept in Deleuze’s philosophy. In several of my posts I am merely using the concept of multiplicity strategically in order to contest the false unity that is often projected onto Deleuze’s work in progress by seeing it as simply reducible to a philosophy of difference.
This is also one way to defend Deleuze from Laruelle’s critiques, which are based on this monistic reduction of Deleuze’s pluralism to a philosophy of difference. I would add that I also refuse the reductive overcoding by means of the « fold », reading it retrospectively as the major concept of Deleuze’s philosophy.
On the question of Deleuze’s third synthesis of time, I accept its futurality but I reject its characterisation as « return ». The attempt to mitigate its incoherence by the denomination « intensive » return is a cop out. Deleuze in his later works keeps the futurality (e.g. in his evocation of a « people to come ») but drops the « return » and de-emphasises « difference », and this is an improvement.
On the question of the treatment of the « eternal return » in RHIZOME: in the introduction to A THOUSAND PLATEAUS, Deleuze and Guattari make a distinction between the figure of the a-centric non-unitary rhizome and figures that apparently renounce unity but that re-constitute it at a higher level. This is the heart of their analysis of the « fascicular » system as opposed to the rhizome.
In this book Deleuze and Guattari analyse the « eternal return » as belonging to the the fascicular mode rather than to the rhizome. Similarly, they consider Burroughs’ « cut-up » as being fascicular, involving a « supplementary dimension » of folding where a spiritual unity persists. In DIALOGUES Deleuze contrasts Burroughs’ cut-up technique with his own « pick-up » method, which involves consistences arising out of contingent encounters.