Can I install reclaimed pine flooring over a floating subfloor?
it does greatly depend on climate, but if this is a slab on grade or a basement slab, you will have issues with wood warpage and expansion cracking from water permeation through the slab, no matter how much of a vapour barrier you install.  you will have to seal the slab with a urethane slab sealer first.  then you can put in drycore or any other type of ventilated subfloor.  

also, you may want to consider that reclaimed pine, although lovely, is one of the worst materials for a kitchen floor.  its too soft and too porous for even sporadic exposure to water.  its a terrible wear surface as well.