Unity saying "don't worry we'll send a bill to Microsoft and Sony and-" has huge Sovereign Citizen Sending Letter Signed In Blood To Reclaim Their Federal Taxes energy. https://twistedvoxel.com/unity-playstation-xbox-nintendo-pay-on-behalf-of-devs/

Of course! Some of the most litigious companies in the world aren't going to take issue with paying for a contract that they weren't a party to. /s
Wouldn't be surprised if Microsoft doesn't just tell Unity to fuck off, but instead assigns a legal team to just make sure no one else gets the same idea again.