There is no single experiment ruling out such a model.
There are conceptual problems. Such as where did the space come from in your model? Or is space curved by your quantum effects (such as a non-zero vacuum energy)?
Spacetime itself does not have to come from somewhere as an emergent concept. It could just be there as it's currently the case with either GR or QFT. Spacetime could get curved via the expectation value of the energy-momentum tensor. No mathemetical ambiguities, no contradiction to experiments, and fully consistent with both GR and the SM. However, I would hardly call this a "unified" description of all forces. Nevertheless, arguing against such a description of nature on purely aesthetic grounds is a bit shaky, IMO.