I myself would be very careful of using that much coconut flour, whatever the ratio you figure out (for one thing, you'll need a LOT more liquid in the recipe, as coconut flour is extremely dry and soaks up moisture like crazy). Once last summer I made some breadsticks with coconut flour, and ate a bit larger portion than I intended (though not a large portion at all, based on eating bread) and it absolutely tore up my guts -- I don't know if it was the fiber or what, but the most agonizing gas pains. I will stick to recipes using at most 2 Tbs. from now on!
Coconut flour is also very high in calories and fat, comparatively, so I'd think that would be a main factor for many gluten intolerant folks. I really don't think it's a good all-around substitute for grain flour, however.