I don't think there's any reason to upgrade unless some of your dependencies require a higher version and backporting is more expensive that porting over all your existing code. Since it sounds like you expose libraries with your own code and you have full control over your ecosystem, I don't think it makes sense to upgrade. At least in my project I see no reason to switch away from LuaJIT (so ~5.1/5.2). It works perfectly well and I don't see why that would change.