Based on my experiences growing both N. northiana and N. burbidgeae from seedlings to mature, flowering plants, I can say that I really don't think limestone in the compost has anything to do with successfully cultivating these species. This does not mean that it does not confer some benefit, only that it does not appear to be at all necessary to produce large, healthy, mature plants.
My compost for these plants consists largely of perlite, charcoal, and fine orchid bark, with a small amount of peat. It's fairly acidic, I'm sure, and I don't think that the specifics of the mixture are that critical, as long as it drains pretty well. Really, I think the key with these plants is simply providing the correct environmental conditions, and in the case of N. northiana, this includes ensuring that the plant does not receive too much light. It's actually quite sensitive to over-exposure.