Actually, you don't owe royalties on "all revenue" with UE4. You only owe royalties on revenues above the first $3,000 per quarter, so you can theoretically earn up to $12,000 per year with UE4 without paying any royalties. Beyond that point, you would start paying some royalties. This arrangement is awesome for indies getting started because it defers the cost of the engine until after you have established some success. I am definitely not saying Unity should eliminate their current options and only offer a subscription with royalties, but I do think Unity would benefit by adding another payment option similar to what Epic is offering. There is a big pricing gap right now between Unity Free and Unity Pro, and Epic's UE4 offering is fitting well in that gap. Unity needs to add a payment option to fill that same gap. Talking about how expensive UE4 could be for people already making six digits is just another way to ignore the real pricing gap issue.