So aside from the additional cost, is there any catch in using it instead of palm oil or tallow, provided you balance it out with a moisturizer like olive oil?
You might get away with just those two, but it would probably yield a very soft bar. A soft bar typically takes longer to cure (be ready to use/sell) and doesn't last as long once it's being used.
In my experience coconut oil, like olive oil, would still need to be mixed with a harder fat like palm or tallow, or hard butters, like cocoa butter. It is on the soft side of oils.
The "old reliable" recipe mixes these three in equal parts: Coconut, Olive, Tallow. Each of them imparts a quality that the others lack. Coconut = cleansing, Olive = moisturizing, Tallow/Palm = Hardness, stability
In my experience coconut oil, like olive oil, would still need to be mixed with a harder fat like palm or tallow, or hard butters, like cocoa butter. It is on the soft side of oils.
The "old reliable" recipe mixes these three in equal parts: Coconut, Olive, Tallow. Each of them imparts a quality that the others lack. Coconut = cleansing, Olive = moisturizing, Tallow/Palm = Hardness, stability