Google already allows/requires tax-exempt donations to not be done with Google Play billing. This doesn't apply in the case of this app because the developer is

Google already allows/requires tax-exempt donations to not be done with Google Play billing. This doesn't apply in the case of this app because the developer is supposedly an individual rather than a non-profit organization. >Or a rule that "donations" are allowed? Well then you get "donations" that come with "bonus functionality" and so forth, and a new line has to be drawn. There really isn't any ambiguity about what constitutes a donation. If you receive something in return, it isn't a donation. I would argue that Google could easily permit donations of any kind at no detriment to themselves.