Yeah, the case that interest me is mobile games with a high install/revenue ratio. If I install a popular game, try it out for 3 minutes, and decide it's not for me, then am I costing some indie developer $0.20 even though there's no revenue?
My guess is that the answer there is in this bit: "Qualifying customers may be eligible for credits toward the Unity Runtime Fee based on the adoption of Unity services beyond the Editor, such as Unity Gaming Services or Unity LevelPlay mediation for mobile ad-supported games. This program enables deeper partnership with Unity to succeed across the entire game lifecycle. Please reach out to your account manager to learn more."
My guess is that as long as Unity is getting a slice of your ads, you don't have to worry about per-install fees. So this may be more about driving free-to-play mobile devs to use their ad services.
Depending on how the legalese is worded, we might also see the comeback of demo versions and paid versions. So the free version has lots of installs but zero revenue, and the $0.20 bite only comes out of things you're charging for.