We thought about it, but the moment you do that, the game is marked as "offers in-app purchases". At initial glance (if you don't take the time to actually look at what purchases are available), you're left thinking that it's "yet another game that'll present a pay wall when I'm about to finish it".
I just bought the game to thank you for no ads, no IAPs.
Have you considered a single IAP that does nothing, but gives you (and Apple, and the IRS) a bit more cash?