The most they’ll have to pay is 20 cents. And that’s only with the 200,000th to 210,000th download for developers who are using the free version of Unity (provided that the developer is also making more then $200k/yr in revenue). After that, the developer will probably get Unity Pro and the download fees will start up at $1 million/yr in revenue and more than 1 million downloads. At that point, I don’t think that the 15 cents to 0.1 cents that will be charged will hurt too badly.