the flat limit of Quantum Gravity will probably not be Minkowski space but the space of an extended special relativity like the Triply Special Relativity that Lee Smolin and Jerzy K-G just posted a paper about "Triply Special Relativity" http://arxiv.org/abs/hep-th/0406276 The idea is analogous to what happend circa 1900 with Singly Special. They took old galilean framework and said "how can we bend this slightly so the speed of light will be the same for all observers?" the coordinate change transformations---the symmetries----are nearly the same as euclidean/galilean except at very high speeds. then you can say what if TWO quantities are the same for all observers. The speed c and also a very small length, like the Planck length? And you can bend Singly Special a little bit to make that happen and you get Doubly special. Now Jerzy K-G and Smolin have addressed the problem of what if you want to have 3 absolute quantities---speed of light, and Planck length AND the cosmological constant. And they bend things just a wee bit more and they get that. It seems like a good candidate for the flat limit of Quantum Gravity doesnt it? And that leaves the question that any mathematician would immediately ask which is "can you go any higher?" Could you futher deform or extend the K-G and S triple relativity so that it becomes quadruple? Well Chryssomalakos and Okun have proven that you cant http://arxiv.org/abs/hep-th/0407080 Triple Relativity is max. From their abstract: "...As a corollary we assure that, within the Lie algebra framework, there is no Quadruply Special Relativity."