I think that kind of business model will screw them. Line has a more sensible one. For example if a business wants to message all its followers, they can only do so twice a month unless they start paying. So customers get an ad-free experience and can only receive ad messages from companies or accounts they follow.
There are most certainly ad banners in Line. At least in Japan. And they used to have some strange invasive bluetooth auto-connect when near a convenience store.
