I'm curious what benefit this would actually yield to you? Is it simply just the case of not having to leave the app? Because aside from that, there would (likely) be no IAP; you'd still be required to give your financial info directly to the app.
I suppose the current situation is that buying is disabled in the app because it is not allowed by Apple (without going trough them and pay the 30% cut), but in an app outside the store it could be enabled.